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Augite-diorite of Camphouse and Faskadale Bay, Ardnamurchan - an excursion

2019-06-26T15:08:01Z

JamesMartin:

File:P000514.jpg

2019-06-26T14:59:55Z

JamesMartin: JamesMartin uploaded a new version of File:P000514.jpg

== Summary ==
Glas Bheinn, Tom a' Chrochaidh, Kilchoan, Ardnamurchan. Argyllshire.

The porphyritic dolerite intrusion extends from Glas Bheinn for 4 km. westwards towards Camphouse. It is one of two porphyritic dolerite intrusions of Centre 1, the other forms a small circular mass south of Ben Hiant. A croft and hayfield are in the foreground. A massive quartz-dolerite cone-sheet of Centre 2 extends obliquely up a hillside cutting through Moine schists in the foreground and a porphyritic dolerite intrusion of Centre 1 of the Ardnamurchan Tertiary igneous complex.

Photographer W Manson
Date 1921
P000514

== Licencing ==
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| Download of 1000 x 1000 pixel images is free for all non-commercial use - all we ask in return is for you to acknowledge BGS when using our images. Click our Terms and Conditions link below for information on acknowledgement text, and to find out about using our images commercially.

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The images may be reproduced free of charge for any non-commercial use in any format or medium provided they are reproduced accurately and not used in a misleading or derogatory context.
Where any images on this site are being republished or copied to others, the source of the material must be identified and the copyright status acknowledged.
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====Non-commercial Use====

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Non-commercial users of the images from this site are restricted to downloading no more than 30 images, without seeking further permission from [mailto:enquiries@bgs.ac.uk enquiries@bgs.ac.uk]

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For commercial use of these images for which higher resolution images are available, individual permissions and/or licences arrangements should be agreed by contacting [mailto:enquiries@bgs.ac.uk enquiries@bgs.ac.uk]

Commercial use will include publications in books (including educational books), newspapers, journals, magazines, CDs and DVDs, etc, where a cover charge is applied; broadcasts on TV, film and theatre; and display in trade fairs, galleries, etc. If you are in doubt as to whether your intended use is commercial, please contact [mailto:enquiries@bgs.ac.uk enquiries@bgs.ac.uk]

====Warranty====
Use of the images downloaded from this site is at the users own risk. UKRI gives no warranty as to the quality of the images or the medium on which they are provided or their suitability for any use.

====Ordnance Survey topography====
Maps and diagrams in Earthwise use topography based on Ordnance Survey mapping. The National Grid and other Ordnance Survey data ©Crown Copyright and database rights 2015. Ordnance Survey Licence No. 100021290 EUL.
|}
[[Category:License tags]]

File:P000514.jpg

2019-06-26T14:34:28Z

JamesMartin: Glas Bheinn, Tom a' Chrochaidh, Kilchoan, Ardnamurchan. Argyllshire. The porphyritic dolerite intrusion extends from Glas Bheinn for 4 km. westwards towards Camphouse. It is one of two porphyritic dolerite intrusions of Centre 1, the other forms a sma...

Drumcarrow and Dura Den - an excursion

2019-06-26T13:50:28Z

JamesMartin:

{{FifeandAngus}}

[[File:_FANG_MAP_13.jpg|thumbnail|Map 13 Drumcarrow - Dura Den.]]

[[File:_FANG_FIG_07.jpg|thumbnail|Figure 7 The flat fields are the site of a former glacial lake near Ceres, seen from Blebo Hole, Pitscottie.]]

[[File:P000913.jpg|thumbnail|Oblique aerial view of Ben Hiant, south coast of Ardnamurchan. Highland Region. Ben Hiant forms an extinct Tertiary volcano, it is the earliest major igneous event of the Ardnamurchan central igneous complex. Photo Christie A)]]

[[File:_FANG_TAB_03.jpg|thumbnail|Table 3 Correlation table for the Old Red Sandstone of Kincardineshire, Tayside and Fife.]]

== ''Excursion 8'' Drumcarrow and Dura Den ==

{| class="wikitable"
|| Duration
|| Half day
|-
| Maps
| OS 1:50,000 map, sheet 59 GS One-inch, 1:50,000, sheets 41, 49
|-
| Excursion map
| [[Media:FANG_MAP_13.jpg|(Map 13)]]
|-
| Walking distance
| 3 km of track and rough road.
|-
| Purpose
| The main objects of this excursion are to examine: (1) some of the Upper Old Red Sandstone sediments in Dura Den; (2) Lower Carboniferous sediments at about the level of the Lower Ardross Limestone (see [[Media:FANG_TAB_05.jpg|(Table 5)]]); (3) the Drumcarrow Olivine–Dolerite Sill; (4) the Blebo Hole Quartz–Dolerite Sill and its contact effects upon the adjacent shales; (5) two small volcanic necks within Kinninmonth Den. Owing to the complex structures and lack of exposures, the Carboniferous rocks have not been subdivided on the Excursion map.
|-
| Route
| Leave St Andrews on the B939 from the West Port and fork left at the University playing fields 1 km further on. Continue past Craigtoun Park to Claremont crossroads [NO 461 146] and there turn left (south then south-west) for 1.5 km along an unclassified road before forking right (west) for 120 m to the track leading up to a quarry on the south face of Drumcarrow Craig. The top of the hill carries a radio mast and a television relay mast.
|}

== 1. Drumcarrow Craig: olivine-dolerite sill ==

The quarry is cut into the Drumcarrow Olivine–Dolerite Sill which is 1.5 km long from east to west and up to 450 m wide from north to south. The majority of exposures of the sill show a well developed columnar jointing while small scarps on the hillside are due to an almost horizontal jointing at right angles to the columnar jointing. In the quarry itself, columnar jointing is prominent and large joint planes normal to the columns (parallel to the intrusion surface) dip steeply southwards. Towards the northern margin of the sill these joint planes are inclined gently north, while at the southern margin they are steeply inclined south. This sill has been classified (Forsyth and Chisholm 1977, p. 141) as a non-ophitic olivine-dolerite, one of a small group in East Fife. In the quarry the rock has a conchoidal fracture and yellow olivines can often be seen on fresh surfaces. Old mining records indicate that the southern side of the sill is strongly transgressive to the local sediments (Forsyth and Chisholm 1977, p. 142).

Ascend to the summit of Drumcarrow Craig, 90 m north of the quarry, for a view of the surrounding geology. The olivinedolerite sill of Denork, also showing good columnar jointing, lies 400 m north-west where it is well exposed in Denork Craig. The low ground to the east is scarred by small tips and shafts from old ironstone workings centred on Denhead and dating from the 19th century. The ironstone, in the Lower Limestone Formation, lies in a faulted NE–SW trending syncline. Apart from the sills, exposure in this area is generally poor. On Drumcarrow Craig east–west glacial striae may be noted on some of the less deeply weathered crags of olivine-dolerite.

== 2. Ladeddie: volcanic vent ==

Return to the bus and continue west for 1.5 km. The western end of the Drumcarrow Sill is cut by an olivine-basalt plug and agglomerate filled vent, just north of Ladeddie Farm. Old quarries in the field are situated where, on a much smaller scale than that of the sill, columnar jointing occurs in the fine-grained basalt.

== 3. Blebo Hole: glacial lakes, drainage channel, quartz-dolerite sill ==

Continue to the T-junction at Backfield of Ladeddie then turn westwards across the bed of a former postglacial lake. The high ground to the north and south of the lake bed is capped by quartz-dolerite sills which form bluffs and crags in several places. At Blebo Hole [NO 423 134], just over 1.5 km west of Backfield of Ladeddie, park at the old farm building and follow the grass track south for 90 m to a quarry in a steep west-facing scarp. To the west is a wide expanse of level ground extending almost to the village of Ceres. This is probably where a mass of dead ice melted forming Glacial Lake Ceres. What was a drainage channel from this lake, now dry, passes the old farm buildings at Blebo Hole, continues north for 400 m, crossing the B939, runs past Blebo House and ultimately joins the Ceres Burn near Kemback. If this interpretation is correct, the present gorge of the Ceres Burn in Dura Den must be a postglacial feature. The burn in the gorge of Kinninmonth Den most probably drained the post-glacial lake to the west of Backfield of Ladeddie.

In the quarry, note the rich yellow-brown soil and subsoil passing down into poorly jointed, spheroidally weathering quartz-dolerite. The rock is coarse grained and contains numerous pink segregation patches. The form of weathering is perhaps the most obvious difference between this quartzdolerite and the olivine-dolerite of Drumcarrow. In addition, iron pyrites is nearly always visible in the hand specimen of the quartz-dolerite, but is rarely seen in the olivine-dolerite (Irving 1929). The segregation patches are notably poor in ferromagnesian minerals.

== 4. Blebo Hole Marine Band ==

Ninety metres south of the quarry, just before the wall which passes in front of the quarry reaches the burn, at the base of a small tree, there is a small outcrop of grey shales dipping to the south-east at 12°: the Blebo Hole Marine Band (Forsyth and Chisholm 1977, p. 48). They are hard and have presumably been thermally metamorphosed by the quartz-dolerite sill. This sill forms the scarp 45 m to the north-east. In the baked shales the fossils have been recrystallised and are now very conspicuous, occurring either as white crystalline calcite with a ferruginous stain, or, if the specimen has been long exposed to weathering, as moulds of the original shells, the calcite having been dissolved out. These shales are believed to be at approximately the same horizon as the shales lying just above the Lower Ardross Limestone. The fauna includes ''Productus, Aviculopecten, Nuculana, Orthoceras, Straparollus, Fenestella, Lithostrotion'' and crinoid ossicles (Craig and Balsillie 1912, p. 12). The marine band is also exposed on the opposite side of the burn, though here it is not as fossiliferous.

== 5. Blebo Hole: volcanic vents ==

If time is available, walk up the north bank of the burn past the previously examined quartz-dolerite sill. In the burn are several small outcrops of Carboniferous rocks lying above the baked shales. One hundred and seventy metres upstream from the shales, notice a white trap dyke exposed in the bed of the burn where it follows an S-bend. Three hundred metres upstream are exposures of a small vent 45 m long and mainly tuff filled, the tuff containing a good deal of little-indurated shale (Craig 1912, p. 84). This rock is similar to that in many other vents in East Fife, but the two dykes that traverse it are relatively unusual (the most obvious of these is exposed in the burn just upstream from a tree which has been blown over and now lies on the fence). The groundmass of the dykes is hard, fine grained and highly altered, consisting of a paste of chlorite and calcite. In it are set xenocrysts of anorthoclase up to 5 cm long, clear and colourless when fresh and yellow or brown when weathered. Large biotite xenocrysts are also common, hornblende xenocrysts rare. Fragments of sandstone and shale are also present, the latter usually surrounded by calcite, while pieces of dark grey glass also occur. A second vent filled with a similar tuff is cut through by the stream 55 m further east, but no dykes are exposed in it. Its eastern contact with the country rock can be seen where shales bend abruptly downwards into the vent, a common feature of such vents owing to drag at the close of eruption when material collapsed back into the vent.

Return to the bus and 90 m west of Blebo Hole, join the B939 for 400 m to Pitscottie crossroads. Note the quartz-dolerite sill exposed on the right, 50 m short of the crossroads. Turn right at the crossroads and immediately right again down Dura Den. For the first 550 m the road crosses a quartz-dolerite sill which is exposed in the Ceres Burn. Eight hundred metres from the crossroads a NNE–SSW fault down-throwing on the east brings in 15 m of horizontal, cross-bedded, creamy sandstone belonging to the Sandy Craig Beds of the Lower Carboniferous (Forsyth and Chisholm 1977, p. 12). Dismount at the weir at Grove Cottage [NO 416 142] and send the bus on for just over 1 km to a small car park past a row of houses and opposite the village hall [NO 416 151].

== 6. Dura Den, Blebo Quarry: quartz-dolerite sill ==

At the roadside north from the weir, another quartz-dolerite sill is split by about 6 m of sandstone which extends east for 400 m. The upper leaf of the sill, now rather altered, may be examined in Blebo Quarry, about 110 m up a narrow path leading north-east from the weir where the path turns sharply right. It is coarse grained and contains pink segregation veins. Now walk northwards along the main road. The sandstone bed which splits the sill crops out on the eastern side of the road, but the contacts with the lower leaf of the sill are not exposed. The first outcrops of the sill are, however, fine grained.

== 7. Dura Den Fault and upturned beds ==

Two hundred and seventy-five metres from the weir, just before a sharp right hand bend in the road, the lower leaf of the sill can be seen upturned against a fault and, beneath it, carbonaceous sandstones with a small coal seam are exposed. Fault drag has increased the dip of these beds to 40° to the south-east in an area of otherwise almost horizontal strata.

== 8. Dura Den: fossil fish locality ==

Follow the road downhill until it meets the Ceres Burn again 450 m below the weir. Sandstones in the bed of the burn at this point belong to the Dura Den Formation of the Stratheden Group (see [[Media:FANG_TAB_03.jpg|(Table 3)]]), formerly simply referred to as the Upper Old Red Sandstone. They form part of the famous Dura Den fossil fish locality. The Dura Den Formation here comprises red, green and cream siltstones alternating with cream coloured sandstones, often with ripple cross bedding (Chisholm and Dean 1974, p. 19). Polygonal mud cracks occur too. The locality was extensively quarried by British Museum collectors (Woodward 1915) and seems to have been completely worked out. Commonest among the fish was ''Holoptychius flemingi'' but several other genera were also present and House ''et al.'' (1977, p. 74) have correlated these beds with the Upper Devonian (Famennian) beds at Clashbenny Quarry on the northern side of the Tay and with other localities in Scotland and Belgium. At the present day sandstones above the old mill lade on the western bank of the burn yield only isolated scales of ''Holoptychius.'' Attridge (1956) found a new locality higher in the succession that has yielded ''Holoptychius,'' but no further discoveries of this kind have been made. No fossils have been recorded from the eastern bank of the burn to date.

== 9. Dura Den: Dura Den Formation (Upper Old Red Sandstone) ==
[[File:P585267.jpg|thumbnail|Dura Den, north Fife; aeolian sandstone of basal Knox Pulpit Formation. P585267.]]
Higher beds of the Dura Den Formation form a high cliff to the east of the road and can be examined 180 to 275 m downstream before reaching a row of cottages and a telephone box between the road and the burn. There is a rough scramble to reach the base of the exposures in the cliff. In the cliff there are 20 m of fine- to very fine-grained, slightly feldspathic sandstones which are in the main plane-bedded, soft, poorly consolidated, and yellow-brown to cream coloured. Some cross bedding occurs and is generally low angled in sets of around 15 cm. Also displayed are ripple marks. These are generally 2.5–5.0 cm in amplitude and asymmetrical. Climbing ripples are rare. Impersistent, thin (2.5 cm), coarser beds of up to granule grade occur as do much harder 10 cm thick nodular calcareous horizons and red-stained silty sandstones. Local erosion surfaces show undercutting. These sandstones appear to be mainly aeolian in origin. Three metres up the cliff and exposed on the underside of a shelf is a mud-flake breccia. This suggests that waterlaid as well as aeolian sediments are present (Hall and Chisholm 1987, p. 204). The nodular calcareous beds here and those at the village hall suggest incipient calcareous soil or 'calcrete' development analogous to that at Bishop Hill (Excursion 17) and fairly widespread in rocks of this age elsewhere in Scotland.

Now continue down to the waterfall just past the village hall. Here the sandstone again shows low angle cross bedding (but in sets up to 1.5 m thick). The sandstone is fine grained and has numerous veins and nodules of calcite.

Rejoin the bus and continue down Dura Den past the old stone bridge over the River Eden [NO 416 161] and continue east for 2.5 km towards Strathkinness.

On the slopes of Knock Hill there are several old overgrown quarries on both sides of the road. These are located in both the Pittenweem Beds and, above, the Sandy Craig Beds of the Strathclyde Group of the Carboniferous (Forsyth and Chisholm 1977, pp. 42–4) and were formerly worked for building stone, much of which can be seen in St Andrews where Geikie (1902, p. 346) remarked on its poor resistance to weathering. Continue eastwards noticing the fine view on the northern side of the road across the Eden Estuary to the Leuchars–Tentsmuir expanse of blown sand. On entering St Andrews, note the University Playing Fields and Observatory standing on a fluvioglacial terrace sloping down eastwards from 30 m to 25 m in a distance of around 1.5 km (Cullingford and Smith 1966, p. 37).

== References ==

ATTRIDGE, J., 1956. A gigantic ''Holoptychius'' from Dura Den. ''Nature Lond.,'' 177, 232–3.

CHISHOLM, J. I. and DEAN, J. M., 1974. The Upper Old Red Sandstone of Fife and Kinross: a fluviatile sequence with evidence of marine incursion. ''Scot. Jour. Geol.,'' 10, 1–30.

CRAIG, R. M., 1912. Additions to the volcanic geology of East Fife. ''Trans. Edinb. Geol. Soc.'' 10, 83–9.

CRAIG, R. M., and BALSILLIE, D., 1912. The Carboniferous rocks and fossils in the neighbourhood of Pitscottie, Fifeshire. ''Trans. Edinb. Geol. Soc.,'' 10, 10–24.

CULLINGFORD, R. A. and SMITH, D. E., 1966. Late-glacial shorelines in Eastern Fife. ''Trans. Inst. Brit. Geogr.,'' 39, 31–51.

FORSYTH, I. H. and CHISHOLM, J. I., 1977. The Geology of East Fife. ''Mem. Geol. Surv. Gt. Brit.''

GEIKIE, A. 1902. The geology of Eastern Fife. ''Mem. Geol. Surv. Scotld.''

HALL, I. H. S. and CHISHOLM, J. I., 1987. Aeolian sediments in the late Devonian of the Scottish Midland Valley. ''Scot. Jour. Geol.,'' 23, 203–8.

HOUSE, M. R. ''et al.,'' 1977. A correlation of Devonian rocks of the British Isles. ''Geol. Soc. Lond. Spec. Rep., No. 7.''

IRVING, J., 1929. The Carboniferous igneous intrusions of North-eastern Fifeshire. ''Unpublished Ph.D. thesis, St Andrews University.''

WOODWARD, A. S., 1915. Preliminary report on the fossil fish from Dura Den. ''Rep. Br. Ass. Advmt. Sci.,'' 1914, 122–4.

{{EGwalks}}
[[Category:5. Midland Valley of Scotland]]

File:P000514.jpeg

2019-06-26T13:49:19Z

JamesMartin: Glas Bheinn, Tom a' Chrochaidh, Kilchoan, Ardnamurchan. Argyllshire. The porphyritic dolerite intrusion extends from Glas Bheinn for 4 km. westwards towards Camphouse. A massive quartz-dolerite cone-sheet of Centre 2 extends obliquely up a hillside...

== Summary ==
Glas Bheinn, Tom a' Chrochaidh, Kilchoan, Ardnamurchan. Argyllshire.

The porphyritic dolerite intrusion extends from Glas Bheinn for 4 km. westwards towards Camphouse. A massive quartz-dolerite cone-sheet of Centre 2 extends obliquely up a hillside cutting through Moine schists in the foreground and a porphyritic dolerite intrusion of Centre 1 of the Ardnamurchan Tertiary igneous complex.

Photographer W Manson.
Date 1921

P000514

== Licencing ==
__notoc__
{|class="wikitable" style="width:100% style="background:#f0f8ff; font-size:80%"
| Download of 1000 x 1000 pixel images is free for all non-commercial use - all we ask in return is for you to acknowledge BGS when using our images. Click our Terms and Conditions link below for information on acknowledgement text, and to find out about using our images commercially.

====Copyright====

The images featured on this site unless otherwise indicated are copyright material of the UK Research and Innovation (UKRI), of which the British Geological Survey is a component body. The British Geological Survey encourages the use of its material in promoting geological and environmental sciences.
The images may be reproduced free of charge for any non-commercial use in any format or medium provided they are reproduced accurately and not used in a misleading or derogatory context.
Where any images on this site are being republished or copied to others, the source of the material must be identified and the copyright status acknowledged.
The permission to reproduce UKRI protected material does not extend to any images on this site which are identified as being the copyright of a third party. Authorisation to reproduce such material must be obtained from the copyright holders concerned.

====Non-commercial Use====

Use of the images downloaded from this site and reproduced digitally or otherwise may only be used for non-commercial purposes, which are:-

* Private study or research for a non-commercial purpose
* Education – for teaching, preparation and examination purposes

When using the images please credit 'British Geological Survey' and include the catalogue reference ('P Number') of the item to allow others to access the original image or document.
Non-commercial users of the images from this site are restricted to downloading no more than 30 images, without seeking further permission from [mailto:enquiries@bgs.ac.uk enquiries@bgs.ac.uk]

====Commercial Use====

For commercial use of these images for which higher resolution images are available, individual permissions and/or licences arrangements should be agreed by contacting [mailto:enquiries@bgs.ac.uk enquiries@bgs.ac.uk]

Commercial use will include publications in books (including educational books), newspapers, journals, magazines, CDs and DVDs, etc, where a cover charge is applied; broadcasts on TV, film and theatre; and display in trade fairs, galleries, etc. If you are in doubt as to whether your intended use is commercial, please contact [mailto:enquiries@bgs.ac.uk enquiries@bgs.ac.uk]

====Warranty====
Use of the images downloaded from this site is at the users own risk. UKRI gives no warranty as to the quality of the images or the medium on which they are provided or their suitability for any use.

====Ordnance Survey topography====
Maps and diagrams in Earthwise use topography based on Ordnance Survey mapping. The National Grid and other Ordnance Survey data ©Crown Copyright and database rights 2015. Ordnance Survey Licence No. 100021290 EUL.
|}
[[Category:License tags]]

Ben Hiant, Ardnamurchan - an excursion

2019-06-26T13:29:03Z

JamesMartin: /* Ben (or Beinn) Hiant - an excursion */

File:P000913.jpg

2019-06-26T13:13:24Z

JamesMartin: Oblique aerial view of Ben Hiant, south coast of Ardnamurchan. Highland Region. Ben Hiant forms an extinct Tertiary volcano, it is the earliest major igneous event of the Ardnamurchan central igneous complex. Oblique aerial view of Ben Hiant, south co...

== Summary ==
Oblique aerial view of Ben Hiant, south coast of Ardnamurchan. Highland Region. Ben Hiant forms an extinct Tertiary volcano, it is the earliest major igneous event of the Ardnamurchan central igneous complex.

Oblique aerial view of Ben Hiant, south coast of Ardnamurchan. Highland Region. Ben Hiant forms an extinct Tertiary volcano, it is the earliest major igneous event of the Ardnamurchan central igneous complex. Much of the activity of this volcano was highly explosive pyroclastic acid magmatism involving the formation of coarse agglomerates erupted in a sub-aerial environment. Later massive intrusions of quartz-dolerite cone-sheets form the main mass of the mountain and the principal intrusions of this early igneous centre on Ardnamurchan.

Photographer: Christie, A.

Date 1977

== Licencing ==
__notoc__
{|class="wikitable" style="width:100% style="background:#f0f8ff; font-size:80%"
| Download of 1000 x 1000 pixel images is free for all non-commercial use - all we ask in return is for you to acknowledge BGS when using our images. Click our Terms and Conditions link below for information on acknowledgement text, and to find out about using our images commercially.

====Copyright====

The images featured on this site unless otherwise indicated are copyright material of the UK Research and Innovation (UKRI), of which the British Geological Survey is a component body. The British Geological Survey encourages the use of its material in promoting geological and environmental sciences.
The images may be reproduced free of charge for any non-commercial use in any format or medium provided they are reproduced accurately and not used in a misleading or derogatory context.
Where any images on this site are being republished or copied to others, the source of the material must be identified and the copyright status acknowledged.
The permission to reproduce UKRI protected material does not extend to any images on this site which are identified as being the copyright of a third party. Authorisation to reproduce such material must be obtained from the copyright holders concerned.

====Non-commercial Use====

Use of the images downloaded from this site and reproduced digitally or otherwise may only be used for non-commercial purposes, which are:-

* Private study or research for a non-commercial purpose
* Education – for teaching, preparation and examination purposes

When using the images please credit 'British Geological Survey' and include the catalogue reference ('P Number') of the item to allow others to access the original image or document.
Non-commercial users of the images from this site are restricted to downloading no more than 30 images, without seeking further permission from [mailto:enquiries@bgs.ac.uk enquiries@bgs.ac.uk]

====Commercial Use====

For commercial use of these images for which higher resolution images are available, individual permissions and/or licences arrangements should be agreed by contacting [mailto:enquiries@bgs.ac.uk enquiries@bgs.ac.uk]

Commercial use will include publications in books (including educational books), newspapers, journals, magazines, CDs and DVDs, etc, where a cover charge is applied; broadcasts on TV, film and theatre; and display in trade fairs, galleries, etc. If you are in doubt as to whether your intended use is commercial, please contact [mailto:enquiries@bgs.ac.uk enquiries@bgs.ac.uk]

====Warranty====
Use of the images downloaded from this site is at the users own risk. UKRI gives no warranty as to the quality of the images or the medium on which they are provided or their suitability for any use.

====Ordnance Survey topography====
Maps and diagrams in Earthwise use topography based on Ordnance Survey mapping. The National Grid and other Ordnance Survey data ©Crown Copyright and database rights 2015. Ordnance Survey Licence No. 100021290 EUL.
|}
[[Category:License tags]]

Kilchoan, Beinn na Seilg and Aodann, Ardnamurchan - an excursion

2019-06-26T12:58:49Z

JamesMartin: /* Kilchoan, Beinn na Seilg and Aodann - Section A */

[[File:EGSArdCover.jpg|250px|thumbnail|Buy the book: [http://www.edinburghgeolsoc.org/p_sales.html#ardnamurchan EGS]]]
'''From: Gribble, C.D., Durrance, E.M. and Walsh, J.N. 1976 [1996 reprint] [[Ardnamurchan – a guide to geological excursions]]. Edinburgh : Edinburgh Geological Society'''

== Kilchoan, Beinn na Seilg and Aodann - introduction ==

The objectives of this excursion are to examine around Kilchoan the effects of thermal alteration both in the host rocks and the included xenoliths of the hypersthene-gabbro of Centre 2, and to observe the relative age relationships and form of the plutonic intrusions of Centre 2 between Beinn na Seilg and Aodann. The internal structure of the hypersthene-gabbro and its contact with the granophyric quartz-dolerite are well displayed on the southern and eastern slopes of Beinn na Seilg, while the relationships between the eucrite of Beinn nan Ord and the quartzgabbros of Beinn na Seilg, Garbh-dhail and Faskadale (Centre 3) are seen on the northern and western slopes. Cone-sheets of the inner suite of Centre 2 cut the quartzgabbro of Garbh-dhail, and the contact of this ring dyke with the older gabbro of Lochan an Aodainn can be observed. The composite nature of the quartz-gabbro of Aodann is also well displayed. A late felsite is seen cutting the Aodann quartz-gabbro, and a pitchstone dyke cuts the hypersthene-gabbro.

Total distance (Kilchoan-Kilchoan) about 17 km, including car travel.

== Kilchoan, Beinn na Seilg and Aodann - Section A ==
[[File:_P253787.jpg|thumbnail| Kilchoan. Cone-sheet cutting Lias west of jetty. Photographer Reynolds Date 1931]]

From the Kilchoan Hotel follow the main road westwards for about 300 m. Vehicles may be parked near the post office.
=== Locality 1 [NM 485 637]. ===
Just beyond the War Memorial, a small roadside exposure reveals amygdaloidal basalt. Although not suitable for collecting material, it is possible to observe that some thermal alteration has occurred, from the presence of a grey weathering product (as opposed to the normal rusty weathering of unaltered basalt). This is probably produced by the hypersthene-gabbro which is some 400 m to the north. A cone-sheet which cuts the basalt sill shows its dark, fine-grained margin.

=== Locality 2 [NM 481 641]. ===
Continue west along the main road, turn right for the lighthouse and proceed as far as the Free Church, where vehicles may be parked. In small exposures above the road, just to the south of the Free Church manse, the cone-sheets can be seen to still possess their dark margins although lying close to the hypersthene-gabbro. The Lower Lias shales which form the host to the cone-sheets are. however. considerably indurated.

=== Locality 3 [NM 479 643]. ===
Further north, immediately beyond the last house on the right of the road. recrystallised conesheets with a new growth of biotite are exposed cutting altered basalts, the amygdales in the basalts being filled with chlorite or plagioclase feldspar. Unaltered porphyritic cone-sheets with well-chilled margins are also present. These may be either part of the inner suite of Centre 2 or part of the Centre 3 suite.

=== Locality 4 [NM 480 647]. ===
Follow the lighthouse road north to the junction for Sanna. Turn right and proceed as far as the permanent caravan site, just before reaching the bridge over the Amhainn Chro Bheinn. Limited parking is possible on the left of the road by the bridge. Joining the road by the entrance to the caravan site is a grassy track. Follow this track, which eventually gives way to a footpath, upstream for about 400 m, until a heavily hammered area on the path is reached. Black xenoliths in which dark green spinel, basic plagioclase, colourless corundum and sapphire occur, are found here as irregular shaped or rounded masses enclosed in a grey, completely recrystallised basic rock. This dark-grey rock is possibly an early consolidated part of the hypersthene-gabbro. A narrow, banded reaction zone, usually only a few centimetres wide, is developed between the sapphire-bearing masses and the grey rock. Normal hypersthene-gabbro occurs a few metres to the north of this locality, while the basalt of Glebe Hill which forms a roof to the gabbro, lies immediately to the south.

== Kilchoan, Beinn na Seilg and Aodann - Section B ==

=== Introduction ===
Return to the junction of the Sanna road with the Lighthouse road and turn right. Continue along the road for about 1.5 km to a point near the southern end of Lochan na Crannaig, where vehicles may be parked in a lay-by on the left of the road. Head south-westwards across country for about 500 m. using the slightly higher ground to skirt to the north-west of a large area of peat, then south-southeast for a further 400 m to the gorge of the Alit Fhearghais (not named on coloured map). Follow the stream southwards for about 700 m to the col between Beinn na Seilg and Stacan Dubha, and thence to the Lochain Ghleann Locha. Proceed to the western end of the strip of land separating the lochs, to examine relationships between the hypersthene-gabbro, basalt and a pitchstone dyke.

=== Locality 5 [NM 463 638]. ===
The outer contact of the hypersthenegabbro passes between the lochs. lying in a hollow. bounded to the south by basalt. Judging by the topographic relationships. the contact dips fairly steeply. Cutting the hypersthene-gabbro is a north-north-west trending pitchstone dyke. This is fairly well exposed near the western end of the south shore of the northern loch, the outcrop displaying the flow-banding characteristic of this particular intrusion.

=== Locality 6 [NM 462 638]. ===
Immediately west of the twin lochs, outcrops of basalt and hypersthene-gabbro occur in close proximity. Again the evidence suggests a steeply dipping contact. In this general area both the hypersthene-gabbro and the basalt are cut by cone-sheets of the outer suite of Centre 2.

=== Locality 7 [NM 462 641]. ===
The col separating Beinn na Seilg and Stacan Dubha has a central ridge of higher ground, with a gully (occupied by the Alit Fhearghais) to the east, and a more gentle depression to the west (this lies due north of the western end of the twin lochs). Head northwards to this depression. Near the highest point of the col, on its western flank, are several outcrops of the pitchstone dyke. Most of these show magnificent examples of contorted flowbanding. Nearby, in the centre of the col depression, dykelike bodies of fine-grained basic rock are present in the hypersthene-gabbro.

=== Locality 8 [NM 464 641]. ===
Skirt around to the south of the ridge of ground east of the col depression and cross the floor of the gully to Stacan Dubha. On the south-west hillside, overlooking the twin lochs, numerous xenolithic bands occur within the hypersthene-gabbro. The bands reach up to 1 m or so across, and keep a constant width for several metres before dying out. They usually dip northwards at about 25°, lying parallel to a mineralogical layering which is developed in the surrounding gabbro. Lithologically, they are dark grey, fine-grained basic rocks, and close in composition to the hypersthene-gabbro itself. Both the xenoliths and surrounding gabbro are cut by a system of acid veins.

=== Locality 9 [NM 465 642]. ===
Just a few metres north of the summit cairns of Stacan Dubha, steeply dipping dyke-like bodies of fine-grained basic rock usually only a few centimetres, but reaching up to 1 m thick, are found to extend through the hypersthene-gabbro for several metres. Some of these appear to have been intruded into the gabbro while the host was still hot, but others are definitely xenolithic.

=== Locality 10 [NM 466 643]. ===
Lying about 150 m north-east of the summit of Stacan Dubha is a marked north-north-west to south-south-east trending gully. North of this gully a number of gabbro-pegmatite bodies occur sporadically within the hypersthene-gabbro. Some of these pegmatites have associated cores of quartz-feldspar rock.

=== Locality 11 [NM 464 643]. ===
Follow the north side of the hill westwards to the crags which overlie the gully of the Alit Fhearghais, and form the north-western flank of the hill. A granophyre sheet is found here intruding the hypersthenegabbro. This is probably. a marginal extension of the granophyric quartz-dolerite which outcrops further west.

=== Locality 12 [NM 457 639]. ===
Return to the south-west side of Stacan Dubha and then head westwards, along the contour to the south slope of Beinn na Seilg. Ascend Beinn na Seilg noting that the outcrops en route show the presence of a complex contact between the hypersthene-gabbro and the granophyric quartz-dolerite. On the higher part of the mountain this contact is flat-lying, the hypersthene-gabbro clearly forming a capping. Southwards too, the sinuosity of the contact and the occurrence of isolated patches of gabbro surrounded by granophyric dolerite show that the hypersthene-gabbro overlies the granophyric dolerite but their contact here must dip southwards at about the same general angle as the topographic slope. Individual contacts. where visible, however, dip both to the north and the south. the northerly dip possibly being produced by the attitude of the layering in the hypersthene-gabbro controlling marginal off-shoots from the upper surface of the granophyric dolerite. Both intrusions are cut by cone-sheets of the inner suite of Centre 2.

=== Locality 13 [NM 457 642]. ===
Cross the summit ridge of Beinn na Seilg between the cairns and ascend the western summit. A magnificent view is afforded of the Inner Hebridean islands, with the Outer Hebrides being visible on a clear day.

=== Locality 14 [NM 457 643]. ===
Descend from the summit ridge to an area of level ground lying north of the western summit. At this point the quartz-gabbro of Beinn na Seilg shows evidence that an olivine-gabbro of eucritic affinities has been profoundly affected by the later intrusion of a granophyric magma, resulting in the production of a quartz-feldspar mesostasis and alteration of the olivine and pyroxene. The granophyric component contains small apatite crystals. The boundary with the granophyric quartz-dolerite appears to dip steeply.

=== Locality 15 [NM 456 645]. ===
Continue northwards to the floor of the col separating the western and northern summits and cross to the western flank of the the mountain. The eucrite of Beinn nan Ord, which outcrops as distinctive icerounded, rusty-brown masses, has steeply dipping contacts with both the quartz-gabbros of Beinn na Seilg and Garbhdhail. A view north-westwards to Beinn nan Ord shows the eucrite clearly extending up through 100 m or so of altitude. The northern summit of Beinn na Seilg is formed by a dyke-like arm of eucrite, with a near-vertical lateral contact against the quartz-gabbro of Garbh-dhail seen just north of the point where the arm leaves the main mass. More or less unbroken outcrops in this area show the arm to be continuous with the ring dyke. Near its contact with the eucrite, the quartz-gabbro of Garbh-dhail becomes rather fine-grained, more basic and brecciated.

=== Locality 16 [NM 457 649]. ===
Return to the col and follow the eastern flank of the northern summit ridge northwards. Here the quartz-gabbro of Garbh-dhail, cut by members of the inner cone-sheet suite of Centre 2 and the arm of eucrite, forms the roof of the quartz-gabbro of Faskadale (Centre 3). The edge of this younger intrusion is marked by a metamorphic zone in the older rocks, which forms a positive topographic feature that extends down the hillside. The top of the intrusion, immediately below this roof, is composed of granophyre, but further downhill the granophyre becomes more basic and grades into a rather acid quartz-gabbro which, in turn, passes into normal quartz-gabbro.

=== Locality 17 [NM 454 647]. ===
From below the eucrite crags of the northern summit ridge of Beinn na Seilg head southwestwards toward the marked fault-controlled valley of Struthan Bhraigh nam Allt which extends north-south along the west flank of the mountain. In the gorge cut by this stream, steeply dipping porphyritic dolerite conesheets cut the quartz-gabbro of Garbh-dhail. Xenoliths of fine-grained basic rock occur in the quartz-gabbro, and acid veins traverse both the xenoliths and the gabbro. These veins also cut the cone-sheets. Locally, the quartzgabbro passes into olivine-bearing gabbro.

=== Locality 18 [NM 452 654]. ===
Follow the valley north for about 500 m to a peat-filled loch basin and then turn north-west for a further 200 m to the hillside on the north-east margin of Garbh-dhail. This hillside forms the southern end of a craggy north-south ridge which lies to the west of Struthan Bhraigh nam Allt. In this area a steep junction between the quartz-gabbro of Garbh-dhail and the older gabbro of Lochan an Aodainn is visible. the quartz-gabbro showing marginal chilling. The older gabbro is characterised by a distinctive black or bluish-black colour on weathered faces. which results from the presence of dark. clouded feldspars. Although the rock has the composition of an olivine-gabbro it often shows coarsely crystalline spots of acid material and granophyre veins. It also contains xenoliths of finegrained material of quartz-dolerite affinities which in places form sheet-like bands. Looking south to the northern summit of Beinn na Seilg, the arm of eucrite can be clearly seen cutting through the quartz-gabbro of Garbh-dhail with a vertical contact.

=== Locality 19 [NM 452 656]. ===
Continue northwards along the ridge until basalt forming the inner margin of the older gabbro is found. To the east the basalt gives way to agglomerate. the fragments in which are similar to those in the vents of Centre 1, and consist of basalt. trachyte, tuff and quartzdolerite. All fragments in the agglomerate show the effects of thermal alteration brought about by the adjacent plutonic intrusions. The basalt is similarly metamorphosed. but retains its major structures.

=== Locality 20 [NM 451 658]. ===
Return to the summit of the ridge and continue north to the crags at its termination, where a small felsite intrusion outcrops. It is a dark-grey, nonporphyritic rock, which on its eastern flank cuts the quanzgabbro of Aodann. Although younger than the plutonic intrusions which are close by, the rock shows signs of thermal alteration, possibly indicating the presence of the Faskadale quartz-gabbro at no great depth below surface. The quartz-gabbro of Aodann, which occurs near the contact, is relatively fine-grained, but contains porphyritic feldspar crystals up to 5 mm long.

=== Locality 21 [NM 457 663). ===
Head eastwards to cross the Struthan Bhraigh nam Allt, and a parallel stream about 100 m further east, and then turn north to the craggy hill that separates Lochan an Aodainn (a loch with a beautiful crescent of waterlilies) from Aodann. In this area the quartz-gabbro of Aodann exhibits an extremely variable texture and composition. A fine-grained facies forms the capping of the hill, but downhill a coarse-grained variety is found. An abrupt change between the two types occurs on the northern and southern slopes of the hill, but on the west the change appears gradational. Two separate phases of emplacement may be present, the fine-grained facies representing the earlier injection. Also. about 250 m east of Aodann at the contact between the coarse and finegrained types. a finely crystalline dark-grey rock, banded with coarser lighter coloured material, is found, which may represent the remains of an even earlier, more basic, phase of intrusion. Occasionally within the gabbro xenolithic strips occur, with patches of fine-grained rock of quartzdolerite affinities.

=== Locality 22 [NM 459 663]. ===
From the summit of the hill head eastwards to a point about 75 m south-west of the Kilchoan-Lighthouse road and 500 m east of Aodann. Here the outer margin of the quartz-gabbro of Aodann forms a rocky feature extending westwards somewhat obliquely to the hillside. Lying topographically below this feature, the Great Eucrite of Centre 3 is seen displaying a typical coarse-grained appearance. Along the contact between these two rock types occurs a fine-grained porphyritic quartzgabbro. This may represent either another facies of the Aodann quartz-gabbro or an early phase of the Great Eucrite. The junction with the Great Eucrite dips at about 70° to the south-west.

{{EGwalks}}

[[Category:3. Palaeogene volcanic districts of Scotland]]

File:P253787.jpg

2019-06-26T12:42:53Z

JamesMartin: JamesMartin uploaded a new version of File:P253787.jpg

== Summary ==
Kilchoan. Cone-sheet cutting Lias west of jetty

Photographer: Reynolds, S.H

Date 1931

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File:P253787.jpg

2019-06-26T12:22:37Z

JamesMartin: Kilchoan. Cone-sheet cutting Lias west of jetty Photographer: Reynolds, S.H Date 1931

Arbroath, Crawton and Stonehaven - an excursion

2019-06-26T11:34:33Z

JamesMartin:

{{FifeandAngus}}

[[File:_FANG_MAP_03.jpg|thumbnail|Map 3 Arbroath and Crawton]]

[[File:_FANG_MAP_04.jpg|thumbnail|Map 4 Stonehaven.]]

[[File:_FANG_FIG_04.jpg|thumbnail|Figure 4 Upper Old Red Sandstone conglomerate and sandstone resting unconformably on south-east-dipping Arbroath Sandstone of the Garvock Group, Lower Old Red Sandstone. N end of Arbroath Promenade.]]

[[File:_FANG_FIG_05.jpg|thumbnail|Figure 5 Garron Point and Craigeven Bay, Stonehaven. The rocks in the foreground and on the point in the distance are largely sheared spilitic lavas belonging to the Highland Border Complex. The pinnacle left of centre is composed of carbonated serpentine 'fault rock' on the line of the Highland Boundary Fault. To the left are slightly metamorphosed greywackes of the Dalradian Southern Highland Group.]]

[[File:P002860.jpg|thumbnail| Whiting Ness, Arbroath, Angus. Unconformity of Upper Devonian upon Lower Devonian (Upper Old Red Sandstone and Lower Old Red Sandstone). P002860. ]]

[[File:P253440.jpg|thumbnail| Cowie. Reticulate weathering of Downtonian sandstone. P253440. ]]

== Excursion 1 Arbroath, Crawton and Stonehaven (whole day) ==
{| class="wikitable"
||Duration
||Whole day
|-
|| Maps
|| OS 1:50,000 Sheets 45, 54 GS One-inch/1:50,000, Sheets 49, 57, 67
|-
| Route maps
| [[Media:FANG_MAP_03.jpg|(Map 3)]], [[Media:FANG_MAP_04.jpg|(Map 4)]].
|-
| Walking distance
| Arbroath, 1 km; Crawton, 1 km; Stonehaven 5 km; all on rocky shore.
|-
| Purpose
| To examine the following: (1) rocks of the Upper Old Red Sandstone and their unconformable relationship to the Lower Old Red Sandstone; (2) some of the Lower Old Red Sandstone rocks of Kincardineshire, particularly the Crawton Basalts, the Downie Point Conglomerate and the Pridolian (late Silurian) Stonehaven Group rocks at Stonehaven; (3) the Highland Boundary Fault and rocks of the Highland Border Complex at Stonehaven. Structurally the route starts on the south-east side of the Sidlaw Anticline, a NE–SW trending structure of Middle Devonian age. This is gradually crossed and beyond Montrose the rocks form part of the parallel Strathmore Syncline. At Stonehaven the steeply dipping north-west limb of this syncline is met where it abuts against the Highland Boundary Fault. Beyond that lie rocks of the Highland Border Complex and the Dalradian metamorphic rocks of the Scottish Highlands.
|-
| Route
| Starting from Dundee travel along A92 to Arbroath. This route crosses gently undulating farmland underlain by Lower Old Red Sandstone sediments and lavas belonging tothe Arbuthnott and Garvock Groups. On reaching Arbroath pass north-east through the town to the promenade and continue along this to the far end [NO 658 411].
|}

== 1. Arbroath: Whiting Ness; Upper Old Red Sandstone unconformity [[Media:FANG_MAP_03.jpg|(Map 3)]] ==

In the cliff at the back of the beach red sandstones and conglomerates of the Upper Old Red Sandstone unconformably overlie red sandstones of the Garvock Group Arbroath Sandstone (Armstrong and Paterson 1970, p. 15). The latter are fine to coarse-grained, pebbly, cross-bedded and with mud-flake conglomerates and belong to the Lower Old Red Sandstone. The line of unconformity can be traced north-east along the cliff for 250 m until at the north end the Upper Old Red Sandstone can be seen to be banked against a cliff of Lower Old Red Sandstone. Armstrong ''et al.'' (1985, p. 51) have deduced a relief of 100 m in the pre-Upper Old Red Sandstone land surface. Within the Upper Old Red Sandstone other sedimentary structures can be seen to advantage. Ramos and Friend (1982, p. 313) believe these to be alluvial plain deposits. A poorly developed cornstone affecting a conglomerate penetrates the unconformity and has developed a network of carbonate veins in the Arbroath Sandstone beneath. The inclination of the Upper Old Red Sandstone is very gentle (10° ESE) while that of the Lower Old Red Sandstone is 15° to 25° SE [[Media:FANG_FIG_04.jpg|(Figure 4)]]. No fossils have been obtained from the Upper Old Red Sandstone and the beds are assigned to this period on lithological grounds only, resembling as they do the fossiliferous Upper Old Red Sandstone of the Carse of Gowrie (Armstrong ''et al.'' 1985, p. 51).

Take the bus north from Arbroath along A92 across very poorly exposed Lower Old Red Sandstone sediments. At Inverkeilor the road rises steeply onto the Ferryden Lavas of the Montrose Volcanic Formation within the Arbuthnott Group. These form higher ground which extends north-east along the strike to the coast just south of Montrose. The low ground of the Montrose Basin is occupied by Quaternary clays and alluvium. These overlie Upper Old Red Sandstone sediments occupying a depression in the unconformity surface over the Lower Old Red Sandstone. Continue north beyond Montrose on A92 until 9 km north of Inverbervie and then at [NO 873 810] take the unclassified road that runs for 1 km south-east to the car park at Crawton Farm on the coast [NO 879 798].

== 2. Crawton: boulder beach and conglomerate cliff [[Media:FANG_MAP_03.jpg|(Map 3)]] ==

At Crawton follow the track that continues south from the end of the road down to the old raised beach cliff. Notice the fine storm beach of boulders derived from the Old Red Sandstone conglomerate. On the west side of Crawton Bay this conglomerate, at the base of the Arbuthnott Group, forms a sheer cliff 30 m high with boulders up to 75 cm in diameter. Well rounded quartzite is the commonest constituent, but boulders of various granites and lavas, including the Crawton Basalts, also occur, together with greywacke, jasper and 'greenstone' probably from the Highland Border Complex.

In a traverse eastwards along the shore four successive lavas are crossed, the Crawton Basalts. The tops of these flows are highly vesicular and slaggy and the bottoms less so. Sandstone veins penetrate the lavas whose tops are usually weathered, eroded and uneven with the intervening conglomerates lying in hollows on their surfaces. The basalts and the underlying conglomerates belong to the Crawton Group of the Lower Old Red Sandstone and they all dip west into the Strathmore Syncline at about 15° (Armstrong and Paterson 1970, p. 9).

== 3. Crawton: Crawton Basalts and interbedded conglomerates ==

The tops of three flows can be examined on the beach, but only that of the third flow can be seen easily at high tide. The centres of the flows are massive, with columnar jointing. They have resisted erosion and form southward-projecting promontories, with the more easily eroded conglomerates forming narrow bays between them. The following succession can be seen, all thicknesses being very approximate:

{| class="wikitable"
|-
||
|| metres
|-
|| Thick conglomerate (Arbuthnott Group)
|| —
|-
| Fourth Crawton Basalt
| 12
|-
| Conglomerate
| 6
|-
| Third Crawton Basalt
|rowspan="3"|15
|-
| Thin intermittent red mudstone
|-
| Second Crawton Basalt
|-
| Conglomerate
| 3
|-
| First Crawton Basalt
| 9
|-
| Thick conglomerate
| —
|-
|}

The flows are of porphyritic olivine-basalt with unusually large tabular plagioclase feldspar phenocrysts up to 2.5 cm across; these have a strong, flow-banded, parallel orientation thus giving the rock the platy habit characteristic of the Craw-ton Basalts.

== 4. Crawton: jointing, amygdales and weathering in basalts ==

At this locality, beside the major NW–SE joint shown on the map, the lowest flow weathers in an unusual manner, the centres of the columns wearing away while the margins stand up to produce a honeycomb rock surface. Campbell (1913, p. 940) believed this to be due to silicification along the joints. The lowest flow also contains exceptionally large amygdales up to 15 cm across. These contain chalcedony, clear quartz, amethyst and calcite.

== 5. Crawton: base of the lowest flow and conglomerate ==

The base of only the lowest flow is clearly exposed and at this locality, which is reached by crossing the gully at locality 4, it is seen to rest on a fairly flat sandstone surface over the conglomerate, with local irregularities. The conglomerate contains a wide variety of rock types in boulders up to 1.8 m in diameter. These include mica-schist, gneisses, schistose grits, quartzite, vein quartz, jasper, pink and grey granites, 'felsite', 'basalt', sandstone and grit. Clast imbrication and cross bedding have been used by Haughton (1988) to demonstrate a southerly and easterly source for much of the Crawton Group conglomerates along the coast. The source area was composed mainly of turbidites cut by calc-alkaline plutonic rocks.

== 6. Crawton: Trollochy ==

On returning to the top of the cliff observe on the shore opposite Crawton Farm a small inlet with vertical sides called Trollochy. A series of closely-spaced E–W vertical faults can be seen at the west end of this inlet and on looking across it from the south side sheared pebbles can be seen on the north face. It is thus apparent that the inlet is due to differential erosion along the faults. The net downthrow is small and to the south – with the eye follow the base of the lava along the cliff. Descend to the head of the inlet where the contact between the base of the First Crawton Basalt and the underlying sediment can be examined. The underlying mudstones are slightly thermally metamorphosed and locally they have been squeezed up into the lava.

A small stream flows over the north edge of the inlet. This is a postglacial stream course, the old course, now filled with till, being apparent 60 m further west. It lay along the line of the prominent NW–SE joint traversing both the conglomerates and the lavas. A blow hole is occasionally active on it at high spring tides.

Continue northwards along A92 and, for the last 1.5 km, A957 to Stonehaven; take the bus down to the harbour and continue eastwards on foot to Downie Point [NO 881 851].

== 7. Stonehaven: Downie Point, conglomerate ==

([[Media:FANG_MAP_04.jpg|(Map 4)]]. The succession for the Stonehaven area will be found on this map.)

The headland is composed of conglomerate at the base of the Dunnottar Group of the Lower Old Red Sandstone (Armstrong and Paterson 1970, p. 7), the Downie Point Conglomerate. It is cut by large joints and is one of Campbell's (1913) 'highland conglomerates', with boulders of meta-quartzite predominating, but accompanied by granites, porphyries, rhyolites and andesites. It is about 170 m thick and has a few impersistent grit bands. The dip is vertical and the top faces south-east, i.e. it lies on the north-western limb of the Strathmore syncline. To the south the conglomerate is succeeded by grey tuffaceous sandstones of the Strathlethan Formation, which have been eroded back to form Strathlethan Bay.

Return to the quarry at the foot of the cliff at Downie Point and examine the base of the conglomerate which can be seen to be remarkably sharply defined. The conglomerate has in fact eroded the sandstones and tuffaceous sandstones of the underlying Carron Formation at the top of the Stonehaven Group. Associated with the tuffaceous sandstones are bands of 'volcanic conglomerate' (Campbell, 1913) in which the pebbles consist predominantly of volcanic rocks, here various acid lavas. In the next quarry to the west cross-bedded red sandstones, at one time worked for building stone, are cut by a 12 m thick late-Carboniferous quartz-dolerite dyke running along the strike. This is cut by calcite veins and is deeply weathered at the margins. It can also be examined on the beach.

== 8. Stonehaven Harbour: Carron Formation sandstones ==

If time is available sandstones of the Carron Formation can be examined on the north side of the harbour. These vertical, often massive, brown-weathering, cross-bedded, micaceous sandstones with thin quartzite-pebble beds strike NE–SW and extend along the shore to the mouth of the Carron Water.

== 9. Cowie Shore; car park ==

Take the bus through Stonehaven to the swimming pool [NO 877 865] and parking place beside the shore. Dismount and send the bus on to the lay-by [NO 886 880] 2 km N of Stonehaven.

== 10. Cowie Harbour; Cowie Formation (730 m) ==

Walk along the shore to the old jetty at Cowie Harbour and follow this out to its seaward end and beyond. There at moderately low tide the highest beds of the Cowie Formation are exposed, namely tuffs and tuffaceous sandstones that overlie the Dictyocaris Member. The latter comprises pale grey micaceous siltstones in a series of red, green and purple ripple-marked sandstones. The relatively rare ''Dictyocaris'' is to be found in the siltstones and the Cowie Harbour Fish Band lies near the base. The rare fauna, including ''Hughmilleria, Kampecaris, Pterygotus, Hemiteleaspis, Pterolepis?'' and ''Traquairaspis,'' indicates a Downtonian or Pridoli (late Silurian) age (Friend and Williams 1978, p. 19). Throughout this shore section the beds dip steeply south-east, or are vertical, and strike northeast. A few metres from the end of the jetty a prominent trench about 10 m wide running along the strike marks the outcrop of a rather soft tuff band cut by a number of small faults. These can best be examined by following a 5 cm band of bright green, chloritic sandstone 2 m below the base of the tuff band. This shows repeated displacements of 1–2 m over a considerable distance along the strike. Just below this sandstone lies a volcanic conglomerate 9 m thick and containing pebbles of andesite and more acid lavas. This conglomerate is underlain by a series of brown-weathering sandstones which continue to the top of the beach. Cowie Harbour to the north-east of the jetty lies on the line of a major tear fault across which correlation has not been established.

== 11. Cowie Shore: sedimentary structures and quartz-porphyry dyke ==

For the next 450 m along HWM the rocks consist of cross-bedded, brown-weathering, micaceous, grey sandstones showing a number of sedimentary structures which include slumping, mud flakes up to 30 cm across and concretions. Two hundred and seventy-five metres from Cowie Harbour a large NW–SE quartz-porphyry dyke complex crosses the shore. It forms a low ridge especially near LWM and can also be traced in the cliff behind HWM at a wooden lookout pole. The dyke is irregular, has several branches and has a reddish, pitted, weathered surface. The fresh rock is pink with creamy feldspars, small micas and quartz crystals, all visible to the naked eye. The dyke has been emplaced along the line of a fault and has baked the surrounding sediment. On the south-west side of the dyke there is a swing in the strike of the beds as they approach the fault, which may imply a dextral displacement.

For the next 350 m to the point at Castle of Cowie, the rocks of the Cowie Formation comprise an alternating series of limonitic weathering and tuffaceous sandstones on the one hand and red mudstones and silty beds on the other, the individual units being generally 1.5–3.0 m thick. The sandstones form ridges and show slumping, ripples and cross bedding and can occasionally be seen to erode the mudstones beneath. The latter are best exposed in the cliff and show sand-filled mud cracks. At the point one mudstone is completely cut out by the overlying sandstone which contains numerous mud flakes. These sandstones and mudstones comprise fining-upward units and form part of a fluvial complex (Friend and Williams 1978, p. 19).

== 12. St Mary's Chapel; basal Old Red Sandstone (Cowie Formation) and unconformity ==

In the bay beneath St Mary's Chapel there is much evidence of minor sinistral and dextral tear faulting, most clearly seen where the faults cross the alternating sandy and muddy beds. The beds strike almost due east-west and the faults strike at about 30° and 110°. For 150 m beyond the point exposures are poor at HWM but thereafter it is noticeable that the higher part of the beach has been levelled more than the lower part of the beach. This is because the volcanics of the Highland Border Complex which form the higher part of the beach are more susceptible to erosion than the Old Red Sandstone rocks lower down. The latter can be seen low on the shore but are better exposed in the cliffs of Slug Head to the east where both they and the underlying volcanics are stained a deep hematitic red colour. The fault rock of the Highland Boundary Fault can be seen high on the cliff on the north side of the bay. It is buff-yellow in colour and thus contrasts strongly with the colour of the volcanics.

== 13. Slug Head: basal Old Red Sandstone and Highland Border Complex volcanics ==

The fault running north-east across the bay beneath St Mary's Chapel cuts the cliff 30 m west of the first point of Slug Head. To the east the basal beds of the Old Red Sandstone Cowie Formation can be seen both in the cliff and on the shore. They include breccias, containing lava fragments from the Highland Border Complex up to 5 cm across, interbedded with siltstones and sandstones. The breccias become less numerous upward in the succession and disappear altogether 75 m above the base. Minor faulting is common and the rocks have been considerably sheared, so much so that the lavas in particular are difficult to identify. When fresh lava can be obtained it is seen to be fine grained, greenish-grey in colour and rather crumbly. Henderson and Robertson (1982, p. 435) stated that the lava chemistry is that of spilitic basalt, i.e. enriched in Na2O.

At Slug Head the unconformity between the Cowie Formation at the base of the Old Red Sandstone and the Highland Border Complex can be seen, but it is difficult to follow in detail. The Old Red Sandstone rocks form a series of pinnacles and crags striking out to sea and dipping south at about 70°. The contact between them and the underlying volcanics lies at the base of the pinnacles and in the cliff behind. The volcanics have an apparent dip to the north-west, but this is probably due to shear planes parallel to the plane of the main Highland Boundary Fault which lies about 100 m to the northwest. Poorly developed pillows are to be seen in a small bay north of that in which the unconformity occurs. They have been affected by shearing adjacent to the Highland Boundary Fault. Near LWM better pillows up to 1 m long are displayed and have clear outlines (Trewin ''et al.'' 1987, p. 272). They should not be hammered. More commonly the lava is crushed and sheared and has largely been converted to chlorite schist, hence the term greenstone, often applied to the rock. The lavas are continuously exposed on the shore as far as Ruthery Head. Small wedges of black siliceous shales, red jasper and chert also occur, along with stringers of the fault rock described below.

== 14. Ruthery Head: Highland Boundary Fault ==

On the north side of Ruthery Head the fault rock crops out on the beach among lava blocks and boulders. It is a dolomitic and siliceous carbonate, yellow-buff in colour both in fresh and weathered specimens and has a streaky appearance. It is cut by numerous carbonate veins and is believed to be a highly altered serpentine now lying in the line of the fault.

Exposures of the fault rock, the volcanics and the associated shales are much better on the north-east side of Craigeven Bay, the large mass of fault rock there being clearly visible from the south-west side. It is 12 m thick, has a sharp 70° north-west-dipping contact with the Dalradian rocks, but a rather diffuse contact with the rocks of the Highland Border Complex on its south-east side.

== 15. Craigeven Bay, north-east side: Highland Border Complex ==

Walk round Craigeven Bay, crossing over Dalradian grits and phyllites of the Southern Highland Group, to the north-east side and cross the thick fault rock. In the small bay 30 m to the south-east the strata dip north-west at about 70°, the cleavage and bedding being coincident. Black shales, some of them pyritous and cherty, can be seen interbedded with the volcanics. Individual beds of shale are up to 60 cm thick. Similar beds nearby have yielded inarticulate brachiopods and other fossils indicating an Ordovician age for the shales and associated volcanics (Curry ''et al.'' 1984).

== 16. Garron Point: Highland Border Complex rocks ==

Further exposures of the volcanics, in a schistose condition and cut by carbonate veins, can be seen by returning to Craigeven Bay and climbing up past an old coastguard but to Garron Point. Many stringers and veins of carbonate cut the volcanics. To the north-west on the Skatie Shore Dalradian rocks are well exposed. A detailed account of these and the section to the north can be obtained in Trewin ''et al.'' (1987).

Return to the road by walking 450 m north along the Skatie Shore to the Den of Cowie, a prominent dry valley spanned by a railway viaduct. Walk up this valley and continue to the road by a footpath which passes under the most northerly arch of the viaduct. The lay-by is 200 m to the south-west towards Stonehaven. The dry valley, occupied by the road, is a glacial overflow channel leading in from the sea at 55 m and running out again to the north at 30 m OD. According to Bremner (1925, p. 36) it was cut by melt water from the sea ice during the retreat of the last major Quaternary ice sheet.

Return to St Andrews by driving back down into Stonehaven; from the lay-by there is no access to the A90 to the north. From Stonehaven take the A90 to Dundee.

== References ==

ARMSTRONG, M. and PATERSON, I.B., 1970. The Lower Old Red Sandstone of the Strathmore Region. ''Rep. Inst. Geol. Sci. No. 70/12''

ARMSTRONG M., PATERSON, I.B., and BROWNE, M.A.E., 1985. Geology of the Perth and Dundee district. ''Mem. Br. Geol. Surv.'' Sheets 48W, 48E, 49.

BREMNER, A., 1925. The glacial geology of the Stonehaven district. ''Trans. Edinb. Geol. Soc. 11,'' 25–41.

CAMPBELL, R., 1913. The geology of southeastern Kincardineshire. ''Trans. Roy. Soc. Edinb.'' 48, 923–60.

CURRY, G.B. ''et al.,'' 1984. Age, evolution and tectonic history of the Highland Border Complex, Scotland. ''Trans. Roy. Soc. Edinb.: Earth Sciences'' 75, 113–33.

FRIEND, P.F. and WILLIAMS B.P.J., 1978. A ''field guide to selected outcrop areas of the Devonian of Scotland, the Welsh Borderland and South Wales.'' Palaeont. Assoc. International Symposium on the Devonian system.

HAUGHTON, P.W.D., 1988. A cryptic Caledonian flysch terrane in Scotland. ''Jour. Geol. Soc. Lond.'' 145, 685–703.

HENDERSON, W.G. and ROBERTSON, A.H.F., 1982. The Highland Border rocks and their relation to marginal basin development in the Scottish Caledonides. ''Jour. Geol. Soc. Lond.'' 139, 433–50.

RAMOS, A. and FRIEND, P.F., 1982. Upper Old Red Sandstone sedimentation near the unconformity at Arbroath. ''Scot. Jour. Geol.'' 18, 297–315.

TREWIN, N.H., KNELLER, B.C. and GILLEN, C. (Eds.), 1987. ''Excursion guide to the geology of the Aberdeen area.'' Scottish Academic Press, Edinburgh.

{{EGwalks}}
[[Category:4. Grampian Highlands]]
[[Category:5. Midland Valley of Scotland]]

File:P253440.jpg

2019-06-26T11:23:09Z

JamesMartin: JamesMartin uploaded a new version of File:P253440.jpg

== Summary ==
Cowie. Reticulate weathering of Downtonian sandstone.

Photographer: Reynolds, S.H.

Date 1913

== Licencing ==
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File:P253440.jpg

2019-06-26T11:00:01Z

JamesMartin: Cowie. Reticulate weathering of Downtonian sandstone. Photographer: Reynolds, S.H. Date 1913

Arbroath, Crawton and Stonehaven - an excursion

2019-06-26T10:42:15Z

JamesMartin:

{{FifeandAngus}}

[[File:_FANG_MAP_03.jpg|thumbnail|Map 3 Arbroath and Crawton]]

[[File:_FANG_MAP_04.jpg|thumbnail|Map 4 Stonehaven.]]

[[File:_FANG_FIG_04.jpg|thumbnail|Figure 4 Upper Old Red Sandstone conglomerate and sandstone resting unconformably on south-east-dipping Arbroath Sandstone of the Garvock Group, Lower Old Red Sandstone. N end of Arbroath Promenade.]]

[[File:_FANG_FIG_05.jpg|thumbnail|Figure 5 Garron Point and Craigeven Bay, Stonehaven. The rocks in the foreground and on the point in the distance are largely sheared spilitic lavas belonging to the Highland Border Complex. The pinnacle left of centre is composed of carbonated serpentine 'fault rock' on the line of the Highland Boundary Fault. To the left are slightly metamorphosed greywackes of the Dalradian Southern Highland Group.]]

[[File:P002860.jpg|thumbnail| Whiting Ness, Arbroath, Angus. Unconformity of Upper Devonian upon Lower Devonian (Upper Old Red Sandstone and Lower Old Red Sandstone). P002860. ]]

== Excursion 1 Arbroath, Crawton and Stonehaven (whole day) ==
{| class="wikitable"
||Duration
||Whole day
|-
|| Maps
|| OS 1:50,000 Sheets 45, 54 GS One-inch/1:50,000, Sheets 49, 57, 67
|-
| Route maps
| [[Media:FANG_MAP_03.jpg|(Map 3)]], [[Media:FANG_MAP_04.jpg|(Map 4)]].
|-
| Walking distance
| Arbroath, 1 km; Crawton, 1 km; Stonehaven 5 km; all on rocky shore.
|-
| Purpose
| To examine the following: (1) rocks of the Upper Old Red Sandstone and their unconformable relationship to the Lower Old Red Sandstone; (2) some of the Lower Old Red Sandstone rocks of Kincardineshire, particularly the Crawton Basalts, the Downie Point Conglomerate and the Pridolian (late Silurian) Stonehaven Group rocks at Stonehaven; (3) the Highland Boundary Fault and rocks of the Highland Border Complex at Stonehaven. Structurally the route starts on the south-east side of the Sidlaw Anticline, a NE–SW trending structure of Middle Devonian age. This is gradually crossed and beyond Montrose the rocks form part of the parallel Strathmore Syncline. At Stonehaven the steeply dipping north-west limb of this syncline is met where it abuts against the Highland Boundary Fault. Beyond that lie rocks of the Highland Border Complex and the Dalradian metamorphic rocks of the Scottish Highlands.
|-
| Route
| Starting from Dundee travel along A92 to Arbroath. This route crosses gently undulating farmland underlain by Lower Old Red Sandstone sediments and lavas belonging tothe Arbuthnott and Garvock Groups. On reaching Arbroath pass north-east through the town to the promenade and continue along this to the far end [NO 658 411].
|}

== 1. Arbroath: Whiting Ness; Upper Old Red Sandstone unconformity [[Media:FANG_MAP_03.jpg|(Map 3)]] ==

In the cliff at the back of the beach red sandstones and conglomerates of the Upper Old Red Sandstone unconformably overlie red sandstones of the Garvock Group Arbroath Sandstone (Armstrong and Paterson 1970, p. 15). The latter are fine to coarse-grained, pebbly, cross-bedded and with mud-flake conglomerates and belong to the Lower Old Red Sandstone. The line of unconformity can be traced north-east along the cliff for 250 m until at the north end the Upper Old Red Sandstone can be seen to be banked against a cliff of Lower Old Red Sandstone. Armstrong ''et al.'' (1985, p. 51) have deduced a relief of 100 m in the pre-Upper Old Red Sandstone land surface. Within the Upper Old Red Sandstone other sedimentary structures can be seen to advantage. Ramos and Friend (1982, p. 313) believe these to be alluvial plain deposits. A poorly developed cornstone affecting a conglomerate penetrates the unconformity and has developed a network of carbonate veins in the Arbroath Sandstone beneath. The inclination of the Upper Old Red Sandstone is very gentle (10° ESE) while that of the Lower Old Red Sandstone is 15° to 25° SE [[Media:FANG_FIG_04.jpg|(Figure 4)]]. No fossils have been obtained from the Upper Old Red Sandstone and the beds are assigned to this period on lithological grounds only, resembling as they do the fossiliferous Upper Old Red Sandstone of the Carse of Gowrie (Armstrong ''et al.'' 1985, p. 51).

Take the bus north from Arbroath along A92 across very poorly exposed Lower Old Red Sandstone sediments. At Inverkeilor the road rises steeply onto the Ferryden Lavas of the Montrose Volcanic Formation within the Arbuthnott Group. These form higher ground which extends north-east along the strike to the coast just south of Montrose. The low ground of the Montrose Basin is occupied by Quaternary clays and alluvium. These overlie Upper Old Red Sandstone sediments occupying a depression in the unconformity surface over the Lower Old Red Sandstone. Continue north beyond Montrose on A92 until 9 km north of Inverbervie and then at [NO 873 810] take the unclassified road that runs for 1 km south-east to the car park at Crawton Farm on the coast [NO 879 798].

== 2. Crawton: boulder beach and conglomerate cliff [[Media:FANG_MAP_03.jpg|(Map 3)]] ==

At Crawton follow the track that continues south from the end of the road down to the old raised beach cliff. Notice the fine storm beach of boulders derived from the Old Red Sandstone conglomerate. On the west side of Crawton Bay this conglomerate, at the base of the Arbuthnott Group, forms a sheer cliff 30 m high with boulders up to 75 cm in diameter. Well rounded quartzite is the commonest constituent, but boulders of various granites and lavas, including the Crawton Basalts, also occur, together with greywacke, jasper and 'greenstone' probably from the Highland Border Complex.

In a traverse eastwards along the shore four successive lavas are crossed, the Crawton Basalts. The tops of these flows are highly vesicular and slaggy and the bottoms less so. Sandstone veins penetrate the lavas whose tops are usually weathered, eroded and uneven with the intervening conglomerates lying in hollows on their surfaces. The basalts and the underlying conglomerates belong to the Crawton Group of the Lower Old Red Sandstone and they all dip west into the Strathmore Syncline at about 15° (Armstrong and Paterson 1970, p. 9).

== 3. Crawton: Crawton Basalts and interbedded conglomerates ==

The tops of three flows can be examined on the beach, but only that of the third flow can be seen easily at high tide. The centres of the flows are massive, with columnar jointing. They have resisted erosion and form southward-projecting promontories, with the more easily eroded conglomerates forming narrow bays between them. The following succession can be seen, all thicknesses being very approximate:

{| class="wikitable"
|-
||
|| metres
|-
|| Thick conglomerate (Arbuthnott Group)
|| —
|-
| Fourth Crawton Basalt
| 12
|-
| Conglomerate
| 6
|-
| Third Crawton Basalt
|rowspan="3"|15
|-
| Thin intermittent red mudstone
|-
| Second Crawton Basalt
|-
| Conglomerate
| 3
|-
| First Crawton Basalt
| 9
|-
| Thick conglomerate
| —
|-
|}

The flows are of porphyritic olivine-basalt with unusually large tabular plagioclase feldspar phenocrysts up to 2.5 cm across; these have a strong, flow-banded, parallel orientation thus giving the rock the platy habit characteristic of the Craw-ton Basalts.

== 4. Crawton: jointing, amygdales and weathering in basalts ==

At this locality, beside the major NW–SE joint shown on the map, the lowest flow weathers in an unusual manner, the centres of the columns wearing away while the margins stand up to produce a honeycomb rock surface. Campbell (1913, p. 940) believed this to be due to silicification along the joints. The lowest flow also contains exceptionally large amygdales up to 15 cm across. These contain chalcedony, clear quartz, amethyst and calcite.

== 5. Crawton: base of the lowest flow and conglomerate ==

The base of only the lowest flow is clearly exposed and at this locality, which is reached by crossing the gully at locality 4, it is seen to rest on a fairly flat sandstone surface over the conglomerate, with local irregularities. The conglomerate contains a wide variety of rock types in boulders up to 1.8 m in diameter. These include mica-schist, gneisses, schistose grits, quartzite, vein quartz, jasper, pink and grey granites, 'felsite', 'basalt', sandstone and grit. Clast imbrication and cross bedding have been used by Haughton (1988) to demonstrate a southerly and easterly source for much of the Crawton Group conglomerates along the coast. The source area was composed mainly of turbidites cut by calc-alkaline plutonic rocks.

== 6. Crawton: Trollochy ==

On returning to the top of the cliff observe on the shore opposite Crawton Farm a small inlet with vertical sides called Trollochy. A series of closely-spaced E–W vertical faults can be seen at the west end of this inlet and on looking across it from the south side sheared pebbles can be seen on the north face. It is thus apparent that the inlet is due to differential erosion along the faults. The net downthrow is small and to the south – with the eye follow the base of the lava along the cliff. Descend to the head of the inlet where the contact between the base of the First Crawton Basalt and the underlying sediment can be examined. The underlying mudstones are slightly thermally metamorphosed and locally they have been squeezed up into the lava.

A small stream flows over the north edge of the inlet. This is a postglacial stream course, the old course, now filled with till, being apparent 60 m further west. It lay along the line of the prominent NW–SE joint traversing both the conglomerates and the lavas. A blow hole is occasionally active on it at high spring tides.

Continue northwards along A92 and, for the last 1.5 km, A957 to Stonehaven; take the bus down to the harbour and continue eastwards on foot to Downie Point [NO 881 851].

== 7. Stonehaven: Downie Point, conglomerate ==

([[Media:FANG_MAP_04.jpg|(Map 4)]]. The succession for the Stonehaven area will be found on this map.)

The headland is composed of conglomerate at the base of the Dunnottar Group of the Lower Old Red Sandstone (Armstrong and Paterson 1970, p. 7), the Downie Point Conglomerate. It is cut by large joints and is one of Campbell's (1913) 'highland conglomerates', with boulders of meta-quartzite predominating, but accompanied by granites, porphyries, rhyolites and andesites. It is about 170 m thick and has a few impersistent grit bands. The dip is vertical and the top faces south-east, i.e. it lies on the north-western limb of the Strathmore syncline. To the south the conglomerate is succeeded by grey tuffaceous sandstones of the Strathlethan Formation, which have been eroded back to form Strathlethan Bay.

Return to the quarry at the foot of the cliff at Downie Point and examine the base of the conglomerate which can be seen to be remarkably sharply defined. The conglomerate has in fact eroded the sandstones and tuffaceous sandstones of the underlying Carron Formation at the top of the Stonehaven Group. Associated with the tuffaceous sandstones are bands of 'volcanic conglomerate' (Campbell, 1913) in which the pebbles consist predominantly of volcanic rocks, here various acid lavas. In the next quarry to the west cross-bedded red sandstones, at one time worked for building stone, are cut by a 12 m thick late-Carboniferous quartz-dolerite dyke running along the strike. This is cut by calcite veins and is deeply weathered at the margins. It can also be examined on the beach.

== 8. Stonehaven Harbour: Carron Formation sandstones ==

If time is available sandstones of the Carron Formation can be examined on the north side of the harbour. These vertical, often massive, brown-weathering, cross-bedded, micaceous sandstones with thin quartzite-pebble beds strike NE–SW and extend along the shore to the mouth of the Carron Water.

== 9. Cowie Shore; car park ==

Take the bus through Stonehaven to the swimming pool [NO 877 865] and parking place beside the shore. Dismount and send the bus on to the lay-by [NO 886 880] 2 km N of Stonehaven.

== 10. Cowie Harbour; Cowie Formation (730 m) ==

Walk along the shore to the old jetty at Cowie Harbour and follow this out to its seaward end and beyond. There at moderately low tide the highest beds of the Cowie Formation are exposed, namely tuffs and tuffaceous sandstones that overlie the Dictyocaris Member. The latter comprises pale grey micaceous siltstones in a series of red, green and purple ripple-marked sandstones. The relatively rare ''Dictyocaris'' is to be found in the siltstones and the Cowie Harbour Fish Band lies near the base. The rare fauna, including ''Hughmilleria, Kampecaris, Pterygotus, Hemiteleaspis, Pterolepis?'' and ''Traquairaspis,'' indicates a Downtonian or Pridoli (late Silurian) age (Friend and Williams 1978, p. 19). Throughout this shore section the beds dip steeply south-east, or are vertical, and strike northeast. A few metres from the end of the jetty a prominent trench about 10 m wide running along the strike marks the outcrop of a rather soft tuff band cut by a number of small faults. These can best be examined by following a 5 cm band of bright green, chloritic sandstone 2 m below the base of the tuff band. This shows repeated displacements of 1–2 m over a considerable distance along the strike. Just below this sandstone lies a volcanic conglomerate 9 m thick and containing pebbles of andesite and more acid lavas. This conglomerate is underlain by a series of brown-weathering sandstones which continue to the top of the beach. Cowie Harbour to the north-east of the jetty lies on the line of a major tear fault across which correlation has not been established.

== 11. Cowie Shore: sedimentary structures and quartz-porphyry dyke ==

For the next 450 m along HWM the rocks consist of cross-bedded, brown-weathering, micaceous, grey sandstones showing a number of sedimentary structures which include slumping, mud flakes up to 30 cm across and concretions. Two hundred and seventy-five metres from Cowie Harbour a large NW–SE quartz-porphyry dyke complex crosses the shore. It forms a low ridge especially near LWM and can also be traced in the cliff behind HWM at a wooden lookout pole. The dyke is irregular, has several branches and has a reddish, pitted, weathered surface. The fresh rock is pink with creamy feldspars, small micas and quartz crystals, all visible to the naked eye. The dyke has been emplaced along the line of a fault and has baked the surrounding sediment. On the south-west side of the dyke there is a swing in the strike of the beds as they approach the fault, which may imply a dextral displacement.

For the next 350 m to the point at Castle of Cowie, the rocks of the Cowie Formation comprise an alternating series of limonitic weathering and tuffaceous sandstones on the one hand and red mudstones and silty beds on the other, the individual units being generally 1.5–3.0 m thick. The sandstones form ridges and show slumping, ripples and cross bedding and can occasionally be seen to erode the mudstones beneath. The latter are best exposed in the cliff and show sand-filled mud cracks. At the point one mudstone is completely cut out by the overlying sandstone which contains numerous mud flakes. These sandstones and mudstones comprise fining-upward units and form part of a fluvial complex (Friend and Williams 1978, p. 19).

== 12. St Mary's Chapel; basal Old Red Sandstone (Cowie Formation) and unconformity ==

In the bay beneath St Mary's Chapel there is much evidence of minor sinistral and dextral tear faulting, most clearly seen where the faults cross the alternating sandy and muddy beds. The beds strike almost due east-west and the faults strike at about 30° and 110°. For 150 m beyond the point exposures are poor at HWM but thereafter it is noticeable that the higher part of the beach has been levelled more than the lower part of the beach. This is because the volcanics of the Highland Border Complex which form the higher part of the beach are more susceptible to erosion than the Old Red Sandstone rocks lower down. The latter can be seen low on the shore but are better exposed in the cliffs of Slug Head to the east where both they and the underlying volcanics are stained a deep hematitic red colour. The fault rock of the Highland Boundary Fault can be seen high on the cliff on the north side of the bay. It is buff-yellow in colour and thus contrasts strongly with the colour of the volcanics.

== 13. Slug Head: basal Old Red Sandstone and Highland Border Complex volcanics ==

The fault running north-east across the bay beneath St Mary's Chapel cuts the cliff 30 m west of the first point of Slug Head. To the east the basal beds of the Old Red Sandstone Cowie Formation can be seen both in the cliff and on the shore. They include breccias, containing lava fragments from the Highland Border Complex up to 5 cm across, interbedded with siltstones and sandstones. The breccias become less numerous upward in the succession and disappear altogether 75 m above the base. Minor faulting is common and the rocks have been considerably sheared, so much so that the lavas in particular are difficult to identify. When fresh lava can be obtained it is seen to be fine grained, greenish-grey in colour and rather crumbly. Henderson and Robertson (1982, p. 435) stated that the lava chemistry is that of spilitic basalt, i.e. enriched in Na2O.

At Slug Head the unconformity between the Cowie Formation at the base of the Old Red Sandstone and the Highland Border Complex can be seen, but it is difficult to follow in detail. The Old Red Sandstone rocks form a series of pinnacles and crags striking out to sea and dipping south at about 70°. The contact between them and the underlying volcanics lies at the base of the pinnacles and in the cliff behind. The volcanics have an apparent dip to the north-west, but this is probably due to shear planes parallel to the plane of the main Highland Boundary Fault which lies about 100 m to the northwest. Poorly developed pillows are to be seen in a small bay north of that in which the unconformity occurs. They have been affected by shearing adjacent to the Highland Boundary Fault. Near LWM better pillows up to 1 m long are displayed and have clear outlines (Trewin ''et al.'' 1987, p. 272). They should not be hammered. More commonly the lava is crushed and sheared and has largely been converted to chlorite schist, hence the term greenstone, often applied to the rock. The lavas are continuously exposed on the shore as far as Ruthery Head. Small wedges of black siliceous shales, red jasper and chert also occur, along with stringers of the fault rock described below.

== 14. Ruthery Head: Highland Boundary Fault ==

On the north side of Ruthery Head the fault rock crops out on the beach among lava blocks and boulders. It is a dolomitic and siliceous carbonate, yellow-buff in colour both in fresh and weathered specimens and has a streaky appearance. It is cut by numerous carbonate veins and is believed to be a highly altered serpentine now lying in the line of the fault.

Exposures of the fault rock, the volcanics and the associated shales are much better on the north-east side of Craigeven Bay, the large mass of fault rock there being clearly visible from the south-west side. It is 12 m thick, has a sharp 70° north-west-dipping contact with the Dalradian rocks, but a rather diffuse contact with the rocks of the Highland Border Complex on its south-east side.

== 15. Craigeven Bay, north-east side: Highland Border Complex ==

Walk round Craigeven Bay, crossing over Dalradian grits and phyllites of the Southern Highland Group, to the north-east side and cross the thick fault rock. In the small bay 30 m to the south-east the strata dip north-west at about 70°, the cleavage and bedding being coincident. Black shales, some of them pyritous and cherty, can be seen interbedded with the volcanics. Individual beds of shale are up to 60 cm thick. Similar beds nearby have yielded inarticulate brachiopods and other fossils indicating an Ordovician age for the shales and associated volcanics (Curry ''et al.'' 1984).

== 16. Garron Point: Highland Border Complex rocks ==

Further exposures of the volcanics, in a schistose condition and cut by carbonate veins, can be seen by returning to Craigeven Bay and climbing up past an old coastguard but to Garron Point. Many stringers and veins of carbonate cut the volcanics. To the north-west on the Skatie Shore Dalradian rocks are well exposed. A detailed account of these and the section to the north can be obtained in Trewin ''et al.'' (1987).

Return to the road by walking 450 m north along the Skatie Shore to the Den of Cowie, a prominent dry valley spanned by a railway viaduct. Walk up this valley and continue to the road by a footpath which passes under the most northerly arch of the viaduct. The lay-by is 200 m to the south-west towards Stonehaven. The dry valley, occupied by the road, is a glacial overflow channel leading in from the sea at 55 m and running out again to the north at 30 m OD. According to Bremner (1925, p. 36) it was cut by melt water from the sea ice during the retreat of the last major Quaternary ice sheet.

Return to St Andrews by driving back down into Stonehaven; from the lay-by there is no access to the A90 to the north. From Stonehaven take the A90 to Dundee.

== References ==

ARMSTRONG, M. and PATERSON, I.B., 1970. The Lower Old Red Sandstone of the Strathmore Region. ''Rep. Inst. Geol. Sci. No. 70/12''

ARMSTRONG M., PATERSON, I.B., and BROWNE, M.A.E., 1985. Geology of the Perth and Dundee district. ''Mem. Br. Geol. Surv.'' Sheets 48W, 48E, 49.

BREMNER, A., 1925. The glacial geology of the Stonehaven district. ''Trans. Edinb. Geol. Soc. 11,'' 25–41.

CAMPBELL, R., 1913. The geology of southeastern Kincardineshire. ''Trans. Roy. Soc. Edinb.'' 48, 923–60.

CURRY, G.B. ''et al.,'' 1984. Age, evolution and tectonic history of the Highland Border Complex, Scotland. ''Trans. Roy. Soc. Edinb.: Earth Sciences'' 75, 113–33.

FRIEND, P.F. and WILLIAMS B.P.J., 1978. A ''field guide to selected outcrop areas of the Devonian of Scotland, the Welsh Borderland and South Wales.'' Palaeont. Assoc. International Symposium on the Devonian system.

HAUGHTON, P.W.D., 1988. A cryptic Caledonian flysch terrane in Scotland. ''Jour. Geol. Soc. Lond.'' 145, 685–703.

HENDERSON, W.G. and ROBERTSON, A.H.F., 1982. The Highland Border rocks and their relation to marginal basin development in the Scottish Caledonides. ''Jour. Geol. Soc. Lond.'' 139, 433–50.

RAMOS, A. and FRIEND, P.F., 1982. Upper Old Red Sandstone sedimentation near the unconformity at Arbroath. ''Scot. Jour. Geol.'' 18, 297–315.

TREWIN, N.H., KNELLER, B.C. and GILLEN, C. (Eds.), 1987. ''Excursion guide to the geology of the Aberdeen area.'' Scottish Academic Press, Edinburgh.

{{EGwalks}}
[[Category:4. Grampian Highlands]]
[[Category:5. Midland Valley of Scotland]]

Arbroath, Crawton and Stonehaven - an excursion

2019-06-26T10:40:36Z

JamesMartin:

{{FifeandAngus}}

[[File:_FANG_MAP_03.jpg|thumbnail|Map 3 Arbroath and Crawton]]

[[File:_FANG_MAP_04.jpg|thumbnail|Map 4 Stonehaven.]]

[[File:_FANG_FIG_04.jpg|thumbnail|Figure 4 Upper Old Red Sandstone conglomerate and sandstone resting unconformably on south-east-dipping Arbroath Sandstone of the Garvock Group, Lower Old Red Sandstone. N end of Arbroath Promenade.]]

[[File:_FANG_FIG_05.jpg|thumbnail|Figure 5 Garron Point and Craigeven Bay, Stonehaven. The rocks in the foreground and on the point in the distance are largely sheared spilitic lavas belonging to the Highland Border Complex. The pinnacle left of centre is composed of carbonated serpentine 'fault rock' on the line of the Highland Boundary Fault. To the left are slightly metamorphosed greywackes of the Dalradian Southern Highland Group.]]

[[File:P002860.jpg|thumbnail| Whiting Ness, Arbroath, Angus. Unconformity of Upper Devonian upon Lower Devonian (Upper Old Red Sandstone and Lower Old Red Sandstone). ]]

== Excursion 1 Arbroath, Crawton and Stonehaven (whole day) ==
{| class="wikitable"
||Duration
||Whole day
|-
|| Maps
|| OS 1:50,000 Sheets 45, 54 GS One-inch/1:50,000, Sheets 49, 57, 67
|-
| Route maps
| [[Media:FANG_MAP_03.jpg|(Map 3)]], [[Media:FANG_MAP_04.jpg|(Map 4)]].
|-
| Walking distance
| Arbroath, 1 km; Crawton, 1 km; Stonehaven 5 km; all on rocky shore.
|-
| Purpose
| To examine the following: (1) rocks of the Upper Old Red Sandstone and their unconformable relationship to the Lower Old Red Sandstone; (2) some of the Lower Old Red Sandstone rocks of Kincardineshire, particularly the Crawton Basalts, the Downie Point Conglomerate and the Pridolian (late Silurian) Stonehaven Group rocks at Stonehaven; (3) the Highland Boundary Fault and rocks of the Highland Border Complex at Stonehaven. Structurally the route starts on the south-east side of the Sidlaw Anticline, a NE–SW trending structure of Middle Devonian age. This is gradually crossed and beyond Montrose the rocks form part of the parallel Strathmore Syncline. At Stonehaven the steeply dipping north-west limb of this syncline is met where it abuts against the Highland Boundary Fault. Beyond that lie rocks of the Highland Border Complex and the Dalradian metamorphic rocks of the Scottish Highlands.
|-
| Route
| Starting from Dundee travel along A92 to Arbroath. This route crosses gently undulating farmland underlain by Lower Old Red Sandstone sediments and lavas belonging tothe Arbuthnott and Garvock Groups. On reaching Arbroath pass north-east through the town to the promenade and continue along this to the far end [NO 658 411].
|}

== 1. Arbroath: Whiting Ness; Upper Old Red Sandstone unconformity [[Media:FANG_MAP_03.jpg|(Map 3)]] ==

In the cliff at the back of the beach red sandstones and conglomerates of the Upper Old Red Sandstone unconformably overlie red sandstones of the Garvock Group Arbroath Sandstone (Armstrong and Paterson 1970, p. 15). The latter are fine to coarse-grained, pebbly, cross-bedded and with mud-flake conglomerates and belong to the Lower Old Red Sandstone. The line of unconformity can be traced north-east along the cliff for 250 m until at the north end the Upper Old Red Sandstone can be seen to be banked against a cliff of Lower Old Red Sandstone. Armstrong ''et al.'' (1985, p. 51) have deduced a relief of 100 m in the pre-Upper Old Red Sandstone land surface. Within the Upper Old Red Sandstone other sedimentary structures can be seen to advantage. Ramos and Friend (1982, p. 313) believe these to be alluvial plain deposits. A poorly developed cornstone affecting a conglomerate penetrates the unconformity and has developed a network of carbonate veins in the Arbroath Sandstone beneath. The inclination of the Upper Old Red Sandstone is very gentle (10° ESE) while that of the Lower Old Red Sandstone is 15° to 25° SE [[Media:FANG_FIG_04.jpg|(Figure 4)]]. No fossils have been obtained from the Upper Old Red Sandstone and the beds are assigned to this period on lithological grounds only, resembling as they do the fossiliferous Upper Old Red Sandstone of the Carse of Gowrie (Armstrong ''et al.'' 1985, p. 51).

Take the bus north from Arbroath along A92 across very poorly exposed Lower Old Red Sandstone sediments. At Inverkeilor the road rises steeply onto the Ferryden Lavas of the Montrose Volcanic Formation within the Arbuthnott Group. These form higher ground which extends north-east along the strike to the coast just south of Montrose. The low ground of the Montrose Basin is occupied by Quaternary clays and alluvium. These overlie Upper Old Red Sandstone sediments occupying a depression in the unconformity surface over the Lower Old Red Sandstone. Continue north beyond Montrose on A92 until 9 km north of Inverbervie and then at [NO 873 810] take the unclassified road that runs for 1 km south-east to the car park at Crawton Farm on the coast [NO 879 798].

== 2. Crawton: boulder beach and conglomerate cliff [[Media:FANG_MAP_03.jpg|(Map 3)]] ==

At Crawton follow the track that continues south from the end of the road down to the old raised beach cliff. Notice the fine storm beach of boulders derived from the Old Red Sandstone conglomerate. On the west side of Crawton Bay this conglomerate, at the base of the Arbuthnott Group, forms a sheer cliff 30 m high with boulders up to 75 cm in diameter. Well rounded quartzite is the commonest constituent, but boulders of various granites and lavas, including the Crawton Basalts, also occur, together with greywacke, jasper and 'greenstone' probably from the Highland Border Complex.

In a traverse eastwards along the shore four successive lavas are crossed, the Crawton Basalts. The tops of these flows are highly vesicular and slaggy and the bottoms less so. Sandstone veins penetrate the lavas whose tops are usually weathered, eroded and uneven with the intervening conglomerates lying in hollows on their surfaces. The basalts and the underlying conglomerates belong to the Crawton Group of the Lower Old Red Sandstone and they all dip west into the Strathmore Syncline at about 15° (Armstrong and Paterson 1970, p. 9).

== 3. Crawton: Crawton Basalts and interbedded conglomerates ==

The tops of three flows can be examined on the beach, but only that of the third flow can be seen easily at high tide. The centres of the flows are massive, with columnar jointing. They have resisted erosion and form southward-projecting promontories, with the more easily eroded conglomerates forming narrow bays between them. The following succession can be seen, all thicknesses being very approximate:

{| class="wikitable"
|-
||
|| metres
|-
|| Thick conglomerate (Arbuthnott Group)
|| —
|-
| Fourth Crawton Basalt
| 12
|-
| Conglomerate
| 6
|-
| Third Crawton Basalt
|rowspan="3"|15
|-
| Thin intermittent red mudstone
|-
| Second Crawton Basalt
|-
| Conglomerate
| 3
|-
| First Crawton Basalt
| 9
|-
| Thick conglomerate
| —
|-
|}

The flows are of porphyritic olivine-basalt with unusually large tabular plagioclase feldspar phenocrysts up to 2.5 cm across; these have a strong, flow-banded, parallel orientation thus giving the rock the platy habit characteristic of the Craw-ton Basalts.

== 4. Crawton: jointing, amygdales and weathering in basalts ==

At this locality, beside the major NW–SE joint shown on the map, the lowest flow weathers in an unusual manner, the centres of the columns wearing away while the margins stand up to produce a honeycomb rock surface. Campbell (1913, p. 940) believed this to be due to silicification along the joints. The lowest flow also contains exceptionally large amygdales up to 15 cm across. These contain chalcedony, clear quartz, amethyst and calcite.

== 5. Crawton: base of the lowest flow and conglomerate ==

The base of only the lowest flow is clearly exposed and at this locality, which is reached by crossing the gully at locality 4, it is seen to rest on a fairly flat sandstone surface over the conglomerate, with local irregularities. The conglomerate contains a wide variety of rock types in boulders up to 1.8 m in diameter. These include mica-schist, gneisses, schistose grits, quartzite, vein quartz, jasper, pink and grey granites, 'felsite', 'basalt', sandstone and grit. Clast imbrication and cross bedding have been used by Haughton (1988) to demonstrate a southerly and easterly source for much of the Crawton Group conglomerates along the coast. The source area was composed mainly of turbidites cut by calc-alkaline plutonic rocks.

== 6. Crawton: Trollochy ==

On returning to the top of the cliff observe on the shore opposite Crawton Farm a small inlet with vertical sides called Trollochy. A series of closely-spaced E–W vertical faults can be seen at the west end of this inlet and on looking across it from the south side sheared pebbles can be seen on the north face. It is thus apparent that the inlet is due to differential erosion along the faults. The net downthrow is small and to the south – with the eye follow the base of the lava along the cliff. Descend to the head of the inlet where the contact between the base of the First Crawton Basalt and the underlying sediment can be examined. The underlying mudstones are slightly thermally metamorphosed and locally they have been squeezed up into the lava.

A small stream flows over the north edge of the inlet. This is a postglacial stream course, the old course, now filled with till, being apparent 60 m further west. It lay along the line of the prominent NW–SE joint traversing both the conglomerates and the lavas. A blow hole is occasionally active on it at high spring tides.

Continue northwards along A92 and, for the last 1.5 km, A957 to Stonehaven; take the bus down to the harbour and continue eastwards on foot to Downie Point [NO 881 851].

== 7. Stonehaven: Downie Point, conglomerate ==

([[Media:FANG_MAP_04.jpg|(Map 4)]]. The succession for the Stonehaven area will be found on this map.)

The headland is composed of conglomerate at the base of the Dunnottar Group of the Lower Old Red Sandstone (Armstrong and Paterson 1970, p. 7), the Downie Point Conglomerate. It is cut by large joints and is one of Campbell's (1913) 'highland conglomerates', with boulders of meta-quartzite predominating, but accompanied by granites, porphyries, rhyolites and andesites. It is about 170 m thick and has a few impersistent grit bands. The dip is vertical and the top faces south-east, i.e. it lies on the north-western limb of the Strathmore syncline. To the south the conglomerate is succeeded by grey tuffaceous sandstones of the Strathlethan Formation, which have been eroded back to form Strathlethan Bay.

Return to the quarry at the foot of the cliff at Downie Point and examine the base of the conglomerate which can be seen to be remarkably sharply defined. The conglomerate has in fact eroded the sandstones and tuffaceous sandstones of the underlying Carron Formation at the top of the Stonehaven Group. Associated with the tuffaceous sandstones are bands of 'volcanic conglomerate' (Campbell, 1913) in which the pebbles consist predominantly of volcanic rocks, here various acid lavas. In the next quarry to the west cross-bedded red sandstones, at one time worked for building stone, are cut by a 12 m thick late-Carboniferous quartz-dolerite dyke running along the strike. This is cut by calcite veins and is deeply weathered at the margins. It can also be examined on the beach.

== 8. Stonehaven Harbour: Carron Formation sandstones ==

If time is available sandstones of the Carron Formation can be examined on the north side of the harbour. These vertical, often massive, brown-weathering, cross-bedded, micaceous sandstones with thin quartzite-pebble beds strike NE–SW and extend along the shore to the mouth of the Carron Water.

== 9. Cowie Shore; car park ==

Take the bus through Stonehaven to the swimming pool [NO 877 865] and parking place beside the shore. Dismount and send the bus on to the lay-by [NO 886 880] 2 km N of Stonehaven.

== 10. Cowie Harbour; Cowie Formation (730 m) ==

Walk along the shore to the old jetty at Cowie Harbour and follow this out to its seaward end and beyond. There at moderately low tide the highest beds of the Cowie Formation are exposed, namely tuffs and tuffaceous sandstones that overlie the Dictyocaris Member. The latter comprises pale grey micaceous siltstones in a series of red, green and purple ripple-marked sandstones. The relatively rare ''Dictyocaris'' is to be found in the siltstones and the Cowie Harbour Fish Band lies near the base. The rare fauna, including ''Hughmilleria, Kampecaris, Pterygotus, Hemiteleaspis, Pterolepis?'' and ''Traquairaspis,'' indicates a Downtonian or Pridoli (late Silurian) age (Friend and Williams 1978, p. 19). Throughout this shore section the beds dip steeply south-east, or are vertical, and strike northeast. A few metres from the end of the jetty a prominent trench about 10 m wide running along the strike marks the outcrop of a rather soft tuff band cut by a number of small faults. These can best be examined by following a 5 cm band of bright green, chloritic sandstone 2 m below the base of the tuff band. This shows repeated displacements of 1–2 m over a considerable distance along the strike. Just below this sandstone lies a volcanic conglomerate 9 m thick and containing pebbles of andesite and more acid lavas. This conglomerate is underlain by a series of brown-weathering sandstones which continue to the top of the beach. Cowie Harbour to the north-east of the jetty lies on the line of a major tear fault across which correlation has not been established.

== 11. Cowie Shore: sedimentary structures and quartz-porphyry dyke ==

For the next 450 m along HWM the rocks consist of cross-bedded, brown-weathering, micaceous, grey sandstones showing a number of sedimentary structures which include slumping, mud flakes up to 30 cm across and concretions. Two hundred and seventy-five metres from Cowie Harbour a large NW–SE quartz-porphyry dyke complex crosses the shore. It forms a low ridge especially near LWM and can also be traced in the cliff behind HWM at a wooden lookout pole. The dyke is irregular, has several branches and has a reddish, pitted, weathered surface. The fresh rock is pink with creamy feldspars, small micas and quartz crystals, all visible to the naked eye. The dyke has been emplaced along the line of a fault and has baked the surrounding sediment. On the south-west side of the dyke there is a swing in the strike of the beds as they approach the fault, which may imply a dextral displacement.

For the next 350 m to the point at Castle of Cowie, the rocks of the Cowie Formation comprise an alternating series of limonitic weathering and tuffaceous sandstones on the one hand and red mudstones and silty beds on the other, the individual units being generally 1.5–3.0 m thick. The sandstones form ridges and show slumping, ripples and cross bedding and can occasionally be seen to erode the mudstones beneath. The latter are best exposed in the cliff and show sand-filled mud cracks. At the point one mudstone is completely cut out by the overlying sandstone which contains numerous mud flakes. These sandstones and mudstones comprise fining-upward units and form part of a fluvial complex (Friend and Williams 1978, p. 19).

== 12. St Mary's Chapel; basal Old Red Sandstone (Cowie Formation) and unconformity ==

In the bay beneath St Mary's Chapel there is much evidence of minor sinistral and dextral tear faulting, most clearly seen where the faults cross the alternating sandy and muddy beds. The beds strike almost due east-west and the faults strike at about 30° and 110°. For 150 m beyond the point exposures are poor at HWM but thereafter it is noticeable that the higher part of the beach has been levelled more than the lower part of the beach. This is because the volcanics of the Highland Border Complex which form the higher part of the beach are more susceptible to erosion than the Old Red Sandstone rocks lower down. The latter can be seen low on the shore but are better exposed in the cliffs of Slug Head to the east where both they and the underlying volcanics are stained a deep hematitic red colour. The fault rock of the Highland Boundary Fault can be seen high on the cliff on the north side of the bay. It is buff-yellow in colour and thus contrasts strongly with the colour of the volcanics.

== 13. Slug Head: basal Old Red Sandstone and Highland Border Complex volcanics ==

The fault running north-east across the bay beneath St Mary's Chapel cuts the cliff 30 m west of the first point of Slug Head. To the east the basal beds of the Old Red Sandstone Cowie Formation can be seen both in the cliff and on the shore. They include breccias, containing lava fragments from the Highland Border Complex up to 5 cm across, interbedded with siltstones and sandstones. The breccias become less numerous upward in the succession and disappear altogether 75 m above the base. Minor faulting is common and the rocks have been considerably sheared, so much so that the lavas in particular are difficult to identify. When fresh lava can be obtained it is seen to be fine grained, greenish-grey in colour and rather crumbly. Henderson and Robertson (1982, p. 435) stated that the lava chemistry is that of spilitic basalt, i.e. enriched in Na2O.

At Slug Head the unconformity between the Cowie Formation at the base of the Old Red Sandstone and the Highland Border Complex can be seen, but it is difficult to follow in detail. The Old Red Sandstone rocks form a series of pinnacles and crags striking out to sea and dipping south at about 70°. The contact between them and the underlying volcanics lies at the base of the pinnacles and in the cliff behind. The volcanics have an apparent dip to the north-west, but this is probably due to shear planes parallel to the plane of the main Highland Boundary Fault which lies about 100 m to the northwest. Poorly developed pillows are to be seen in a small bay north of that in which the unconformity occurs. They have been affected by shearing adjacent to the Highland Boundary Fault. Near LWM better pillows up to 1 m long are displayed and have clear outlines (Trewin ''et al.'' 1987, p. 272). They should not be hammered. More commonly the lava is crushed and sheared and has largely been converted to chlorite schist, hence the term greenstone, often applied to the rock. The lavas are continuously exposed on the shore as far as Ruthery Head. Small wedges of black siliceous shales, red jasper and chert also occur, along with stringers of the fault rock described below.

== 14. Ruthery Head: Highland Boundary Fault ==

On the north side of Ruthery Head the fault rock crops out on the beach among lava blocks and boulders. It is a dolomitic and siliceous carbonate, yellow-buff in colour both in fresh and weathered specimens and has a streaky appearance. It is cut by numerous carbonate veins and is believed to be a highly altered serpentine now lying in the line of the fault.

Exposures of the fault rock, the volcanics and the associated shales are much better on the north-east side of Craigeven Bay, the large mass of fault rock there being clearly visible from the south-west side. It is 12 m thick, has a sharp 70° north-west-dipping contact with the Dalradian rocks, but a rather diffuse contact with the rocks of the Highland Border Complex on its south-east side.

== 15. Craigeven Bay, north-east side: Highland Border Complex ==

Walk round Craigeven Bay, crossing over Dalradian grits and phyllites of the Southern Highland Group, to the north-east side and cross the thick fault rock. In the small bay 30 m to the south-east the strata dip north-west at about 70°, the cleavage and bedding being coincident. Black shales, some of them pyritous and cherty, can be seen interbedded with the volcanics. Individual beds of shale are up to 60 cm thick. Similar beds nearby have yielded inarticulate brachiopods and other fossils indicating an Ordovician age for the shales and associated volcanics (Curry ''et al.'' 1984).

== 16. Garron Point: Highland Border Complex rocks ==

Further exposures of the volcanics, in a schistose condition and cut by carbonate veins, can be seen by returning to Craigeven Bay and climbing up past an old coastguard but to Garron Point. Many stringers and veins of carbonate cut the volcanics. To the north-west on the Skatie Shore Dalradian rocks are well exposed. A detailed account of these and the section to the north can be obtained in Trewin ''et al.'' (1987).

Return to the road by walking 450 m north along the Skatie Shore to the Den of Cowie, a prominent dry valley spanned by a railway viaduct. Walk up this valley and continue to the road by a footpath which passes under the most northerly arch of the viaduct. The lay-by is 200 m to the south-west towards Stonehaven. The dry valley, occupied by the road, is a glacial overflow channel leading in from the sea at 55 m and running out again to the north at 30 m OD. According to Bremner (1925, p. 36) it was cut by melt water from the sea ice during the retreat of the last major Quaternary ice sheet.

Return to St Andrews by driving back down into Stonehaven; from the lay-by there is no access to the A90 to the north. From Stonehaven take the A90 to Dundee.

== References ==

ARMSTRONG, M. and PATERSON, I.B., 1970. The Lower Old Red Sandstone of the Strathmore Region. ''Rep. Inst. Geol. Sci. No. 70/12''

ARMSTRONG M., PATERSON, I.B., and BROWNE, M.A.E., 1985. Geology of the Perth and Dundee district. ''Mem. Br. Geol. Surv.'' Sheets 48W, 48E, 49.

BREMNER, A., 1925. The glacial geology of the Stonehaven district. ''Trans. Edinb. Geol. Soc. 11,'' 25–41.

CAMPBELL, R., 1913. The geology of southeastern Kincardineshire. ''Trans. Roy. Soc. Edinb.'' 48, 923–60.

CURRY, G.B. ''et al.,'' 1984. Age, evolution and tectonic history of the Highland Border Complex, Scotland. ''Trans. Roy. Soc. Edinb.: Earth Sciences'' 75, 113–33.

FRIEND, P.F. and WILLIAMS B.P.J., 1978. A ''field guide to selected outcrop areas of the Devonian of Scotland, the Welsh Borderland and South Wales.'' Palaeont. Assoc. International Symposium on the Devonian system.

HAUGHTON, P.W.D., 1988. A cryptic Caledonian flysch terrane in Scotland. ''Jour. Geol. Soc. Lond.'' 145, 685–703.

HENDERSON, W.G. and ROBERTSON, A.H.F., 1982. The Highland Border rocks and their relation to marginal basin development in the Scottish Caledonides. ''Jour. Geol. Soc. Lond.'' 139, 433–50.

RAMOS, A. and FRIEND, P.F., 1982. Upper Old Red Sandstone sedimentation near the unconformity at Arbroath. ''Scot. Jour. Geol.'' 18, 297–315.

TREWIN, N.H., KNELLER, B.C. and GILLEN, C. (Eds.), 1987. ''Excursion guide to the geology of the Aberdeen area.'' Scottish Academic Press, Edinburgh.

{{EGwalks}}
[[Category:4. Grampian Highlands]]
[[Category:5. Midland Valley of Scotland]]

Arbroath, Crawton and Stonehaven - an excursion

2019-06-26T10:39:23Z

JamesMartin:

{{FifeandAngus}}

[[File:_FANG_MAP_03.jpg|thumbnail|Map 3 Arbroath and Crawton]]

[[File:_FANG_MAP_04.jpg|thumbnail|Map 4 Stonehaven.]]

[[File:_FANG_FIG_04.jpg|thumbnail|Figure 4 Upper Old Red Sandstone conglomerate and sandstone resting unconformably on south-east-dipping Arbroath Sandstone of the Garvock Group, Lower Old Red Sandstone. N end of Arbroath Promenade.]]

[[File:_FANG_FIG_05.jpg|thumbnail|Figure 5 Garron Point and Craigeven Bay, Stonehaven. The rocks in the foreground and on the point in the distance are largely sheared spilitic lavas belonging to the Highland Border Complex. The pinnacle left of centre is composed of carbonated serpentine 'fault rock' on the line of the Highland Boundary Fault. To the left are slightly metamorphosed greywackes of the Dalradian Southern Highland Group.]]

[[File:P002860.jpg|thumbnail|Map 4 Stonehaven.]]

== Excursion 1 Arbroath, Crawton and Stonehaven (whole day) ==
{| class="wikitable"
||Duration
||Whole day
|-
|| Maps
|| OS 1:50,000 Sheets 45, 54 GS One-inch/1:50,000, Sheets 49, 57, 67
|-
| Route maps
| [[Media:FANG_MAP_03.jpg|(Map 3)]], [[Media:FANG_MAP_04.jpg|(Map 4)]].
|-
| Walking distance
| Arbroath, 1 km; Crawton, 1 km; Stonehaven 5 km; all on rocky shore.
|-
| Purpose
| To examine the following: (1) rocks of the Upper Old Red Sandstone and their unconformable relationship to the Lower Old Red Sandstone; (2) some of the Lower Old Red Sandstone rocks of Kincardineshire, particularly the Crawton Basalts, the Downie Point Conglomerate and the Pridolian (late Silurian) Stonehaven Group rocks at Stonehaven; (3) the Highland Boundary Fault and rocks of the Highland Border Complex at Stonehaven. Structurally the route starts on the south-east side of the Sidlaw Anticline, a NE–SW trending structure of Middle Devonian age. This is gradually crossed and beyond Montrose the rocks form part of the parallel Strathmore Syncline. At Stonehaven the steeply dipping north-west limb of this syncline is met where it abuts against the Highland Boundary Fault. Beyond that lie rocks of the Highland Border Complex and the Dalradian metamorphic rocks of the Scottish Highlands.
|-
| Route
| Starting from Dundee travel along A92 to Arbroath. This route crosses gently undulating farmland underlain by Lower Old Red Sandstone sediments and lavas belonging tothe Arbuthnott and Garvock Groups. On reaching Arbroath pass north-east through the town to the promenade and continue along this to the far end [NO 658 411].
|}

== 1. Arbroath: Whiting Ness; Upper Old Red Sandstone unconformity [[Media:FANG_MAP_03.jpg|(Map 3)]] ==

In the cliff at the back of the beach red sandstones and conglomerates of the Upper Old Red Sandstone unconformably overlie red sandstones of the Garvock Group Arbroath Sandstone (Armstrong and Paterson 1970, p. 15). The latter are fine to coarse-grained, pebbly, cross-bedded and with mud-flake conglomerates and belong to the Lower Old Red Sandstone. The line of unconformity can be traced north-east along the cliff for 250 m until at the north end the Upper Old Red Sandstone can be seen to be banked against a cliff of Lower Old Red Sandstone. Armstrong ''et al.'' (1985, p. 51) have deduced a relief of 100 m in the pre-Upper Old Red Sandstone land surface. Within the Upper Old Red Sandstone other sedimentary structures can be seen to advantage. Ramos and Friend (1982, p. 313) believe these to be alluvial plain deposits. A poorly developed cornstone affecting a conglomerate penetrates the unconformity and has developed a network of carbonate veins in the Arbroath Sandstone beneath. The inclination of the Upper Old Red Sandstone is very gentle (10° ESE) while that of the Lower Old Red Sandstone is 15° to 25° SE [[Media:FANG_FIG_04.jpg|(Figure 4)]]. No fossils have been obtained from the Upper Old Red Sandstone and the beds are assigned to this period on lithological grounds only, resembling as they do the fossiliferous Upper Old Red Sandstone of the Carse of Gowrie (Armstrong ''et al.'' 1985, p. 51).

Take the bus north from Arbroath along A92 across very poorly exposed Lower Old Red Sandstone sediments. At Inverkeilor the road rises steeply onto the Ferryden Lavas of the Montrose Volcanic Formation within the Arbuthnott Group. These form higher ground which extends north-east along the strike to the coast just south of Montrose. The low ground of the Montrose Basin is occupied by Quaternary clays and alluvium. These overlie Upper Old Red Sandstone sediments occupying a depression in the unconformity surface over the Lower Old Red Sandstone. Continue north beyond Montrose on A92 until 9 km north of Inverbervie and then at [NO 873 810] take the unclassified road that runs for 1 km south-east to the car park at Crawton Farm on the coast [NO 879 798].

== 2. Crawton: boulder beach and conglomerate cliff [[Media:FANG_MAP_03.jpg|(Map 3)]] ==

At Crawton follow the track that continues south from the end of the road down to the old raised beach cliff. Notice the fine storm beach of boulders derived from the Old Red Sandstone conglomerate. On the west side of Crawton Bay this conglomerate, at the base of the Arbuthnott Group, forms a sheer cliff 30 m high with boulders up to 75 cm in diameter. Well rounded quartzite is the commonest constituent, but boulders of various granites and lavas, including the Crawton Basalts, also occur, together with greywacke, jasper and 'greenstone' probably from the Highland Border Complex.

In a traverse eastwards along the shore four successive lavas are crossed, the Crawton Basalts. The tops of these flows are highly vesicular and slaggy and the bottoms less so. Sandstone veins penetrate the lavas whose tops are usually weathered, eroded and uneven with the intervening conglomerates lying in hollows on their surfaces. The basalts and the underlying conglomerates belong to the Crawton Group of the Lower Old Red Sandstone and they all dip west into the Strathmore Syncline at about 15° (Armstrong and Paterson 1970, p. 9).

== 3. Crawton: Crawton Basalts and interbedded conglomerates ==

The tops of three flows can be examined on the beach, but only that of the third flow can be seen easily at high tide. The centres of the flows are massive, with columnar jointing. They have resisted erosion and form southward-projecting promontories, with the more easily eroded conglomerates forming narrow bays between them. The following succession can be seen, all thicknesses being very approximate:

{| class="wikitable"
|-
||
|| metres
|-
|| Thick conglomerate (Arbuthnott Group)
|| —
|-
| Fourth Crawton Basalt
| 12
|-
| Conglomerate
| 6
|-
| Third Crawton Basalt
|rowspan="3"|15
|-
| Thin intermittent red mudstone
|-
| Second Crawton Basalt
|-
| Conglomerate
| 3
|-
| First Crawton Basalt
| 9
|-
| Thick conglomerate
| —
|-
|}

The flows are of porphyritic olivine-basalt with unusually large tabular plagioclase feldspar phenocrysts up to 2.5 cm across; these have a strong, flow-banded, parallel orientation thus giving the rock the platy habit characteristic of the Craw-ton Basalts.

== 4. Crawton: jointing, amygdales and weathering in basalts ==

At this locality, beside the major NW–SE joint shown on the map, the lowest flow weathers in an unusual manner, the centres of the columns wearing away while the margins stand up to produce a honeycomb rock surface. Campbell (1913, p. 940) believed this to be due to silicification along the joints. The lowest flow also contains exceptionally large amygdales up to 15 cm across. These contain chalcedony, clear quartz, amethyst and calcite.

== 5. Crawton: base of the lowest flow and conglomerate ==

The base of only the lowest flow is clearly exposed and at this locality, which is reached by crossing the gully at locality 4, it is seen to rest on a fairly flat sandstone surface over the conglomerate, with local irregularities. The conglomerate contains a wide variety of rock types in boulders up to 1.8 m in diameter. These include mica-schist, gneisses, schistose grits, quartzite, vein quartz, jasper, pink and grey granites, 'felsite', 'basalt', sandstone and grit. Clast imbrication and cross bedding have been used by Haughton (1988) to demonstrate a southerly and easterly source for much of the Crawton Group conglomerates along the coast. The source area was composed mainly of turbidites cut by calc-alkaline plutonic rocks.

== 6. Crawton: Trollochy ==

On returning to the top of the cliff observe on the shore opposite Crawton Farm a small inlet with vertical sides called Trollochy. A series of closely-spaced E–W vertical faults can be seen at the west end of this inlet and on looking across it from the south side sheared pebbles can be seen on the north face. It is thus apparent that the inlet is due to differential erosion along the faults. The net downthrow is small and to the south – with the eye follow the base of the lava along the cliff. Descend to the head of the inlet where the contact between the base of the First Crawton Basalt and the underlying sediment can be examined. The underlying mudstones are slightly thermally metamorphosed and locally they have been squeezed up into the lava.

A small stream flows over the north edge of the inlet. This is a postglacial stream course, the old course, now filled with till, being apparent 60 m further west. It lay along the line of the prominent NW–SE joint traversing both the conglomerates and the lavas. A blow hole is occasionally active on it at high spring tides.

Continue northwards along A92 and, for the last 1.5 km, A957 to Stonehaven; take the bus down to the harbour and continue eastwards on foot to Downie Point [NO 881 851].

== 7. Stonehaven: Downie Point, conglomerate ==

([[Media:FANG_MAP_04.jpg|(Map 4)]]. The succession for the Stonehaven area will be found on this map.)

The headland is composed of conglomerate at the base of the Dunnottar Group of the Lower Old Red Sandstone (Armstrong and Paterson 1970, p. 7), the Downie Point Conglomerate. It is cut by large joints and is one of Campbell's (1913) 'highland conglomerates', with boulders of meta-quartzite predominating, but accompanied by granites, porphyries, rhyolites and andesites. It is about 170 m thick and has a few impersistent grit bands. The dip is vertical and the top faces south-east, i.e. it lies on the north-western limb of the Strathmore syncline. To the south the conglomerate is succeeded by grey tuffaceous sandstones of the Strathlethan Formation, which have been eroded back to form Strathlethan Bay.

Return to the quarry at the foot of the cliff at Downie Point and examine the base of the conglomerate which can be seen to be remarkably sharply defined. The conglomerate has in fact eroded the sandstones and tuffaceous sandstones of the underlying Carron Formation at the top of the Stonehaven Group. Associated with the tuffaceous sandstones are bands of 'volcanic conglomerate' (Campbell, 1913) in which the pebbles consist predominantly of volcanic rocks, here various acid lavas. In the next quarry to the west cross-bedded red sandstones, at one time worked for building stone, are cut by a 12 m thick late-Carboniferous quartz-dolerite dyke running along the strike. This is cut by calcite veins and is deeply weathered at the margins. It can also be examined on the beach.

== 8. Stonehaven Harbour: Carron Formation sandstones ==

If time is available sandstones of the Carron Formation can be examined on the north side of the harbour. These vertical, often massive, brown-weathering, cross-bedded, micaceous sandstones with thin quartzite-pebble beds strike NE–SW and extend along the shore to the mouth of the Carron Water.

== 9. Cowie Shore; car park ==

Take the bus through Stonehaven to the swimming pool [NO 877 865] and parking place beside the shore. Dismount and send the bus on to the lay-by [NO 886 880] 2 km N of Stonehaven.

== 10. Cowie Harbour; Cowie Formation (730 m) ==

Walk along the shore to the old jetty at Cowie Harbour and follow this out to its seaward end and beyond. There at moderately low tide the highest beds of the Cowie Formation are exposed, namely tuffs and tuffaceous sandstones that overlie the Dictyocaris Member. The latter comprises pale grey micaceous siltstones in a series of red, green and purple ripple-marked sandstones. The relatively rare ''Dictyocaris'' is to be found in the siltstones and the Cowie Harbour Fish Band lies near the base. The rare fauna, including ''Hughmilleria, Kampecaris, Pterygotus, Hemiteleaspis, Pterolepis?'' and ''Traquairaspis,'' indicates a Downtonian or Pridoli (late Silurian) age (Friend and Williams 1978, p. 19). Throughout this shore section the beds dip steeply south-east, or are vertical, and strike northeast. A few metres from the end of the jetty a prominent trench about 10 m wide running along the strike marks the outcrop of a rather soft tuff band cut by a number of small faults. These can best be examined by following a 5 cm band of bright green, chloritic sandstone 2 m below the base of the tuff band. This shows repeated displacements of 1–2 m over a considerable distance along the strike. Just below this sandstone lies a volcanic conglomerate 9 m thick and containing pebbles of andesite and more acid lavas. This conglomerate is underlain by a series of brown-weathering sandstones which continue to the top of the beach. Cowie Harbour to the north-east of the jetty lies on the line of a major tear fault across which correlation has not been established.

== 11. Cowie Shore: sedimentary structures and quartz-porphyry dyke ==

For the next 450 m along HWM the rocks consist of cross-bedded, brown-weathering, micaceous, grey sandstones showing a number of sedimentary structures which include slumping, mud flakes up to 30 cm across and concretions. Two hundred and seventy-five metres from Cowie Harbour a large NW–SE quartz-porphyry dyke complex crosses the shore. It forms a low ridge especially near LWM and can also be traced in the cliff behind HWM at a wooden lookout pole. The dyke is irregular, has several branches and has a reddish, pitted, weathered surface. The fresh rock is pink with creamy feldspars, small micas and quartz crystals, all visible to the naked eye. The dyke has been emplaced along the line of a fault and has baked the surrounding sediment. On the south-west side of the dyke there is a swing in the strike of the beds as they approach the fault, which may imply a dextral displacement.

For the next 350 m to the point at Castle of Cowie, the rocks of the Cowie Formation comprise an alternating series of limonitic weathering and tuffaceous sandstones on the one hand and red mudstones and silty beds on the other, the individual units being generally 1.5–3.0 m thick. The sandstones form ridges and show slumping, ripples and cross bedding and can occasionally be seen to erode the mudstones beneath. The latter are best exposed in the cliff and show sand-filled mud cracks. At the point one mudstone is completely cut out by the overlying sandstone which contains numerous mud flakes. These sandstones and mudstones comprise fining-upward units and form part of a fluvial complex (Friend and Williams 1978, p. 19).

== 12. St Mary's Chapel; basal Old Red Sandstone (Cowie Formation) and unconformity ==

In the bay beneath St Mary's Chapel there is much evidence of minor sinistral and dextral tear faulting, most clearly seen where the faults cross the alternating sandy and muddy beds. The beds strike almost due east-west and the faults strike at about 30° and 110°. For 150 m beyond the point exposures are poor at HWM but thereafter it is noticeable that the higher part of the beach has been levelled more than the lower part of the beach. This is because the volcanics of the Highland Border Complex which form the higher part of the beach are more susceptible to erosion than the Old Red Sandstone rocks lower down. The latter can be seen low on the shore but are better exposed in the cliffs of Slug Head to the east where both they and the underlying volcanics are stained a deep hematitic red colour. The fault rock of the Highland Boundary Fault can be seen high on the cliff on the north side of the bay. It is buff-yellow in colour and thus contrasts strongly with the colour of the volcanics.

== 13. Slug Head: basal Old Red Sandstone and Highland Border Complex volcanics ==

The fault running north-east across the bay beneath St Mary's Chapel cuts the cliff 30 m west of the first point of Slug Head. To the east the basal beds of the Old Red Sandstone Cowie Formation can be seen both in the cliff and on the shore. They include breccias, containing lava fragments from the Highland Border Complex up to 5 cm across, interbedded with siltstones and sandstones. The breccias become less numerous upward in the succession and disappear altogether 75 m above the base. Minor faulting is common and the rocks have been considerably sheared, so much so that the lavas in particular are difficult to identify. When fresh lava can be obtained it is seen to be fine grained, greenish-grey in colour and rather crumbly. Henderson and Robertson (1982, p. 435) stated that the lava chemistry is that of spilitic basalt, i.e. enriched in Na2O.

At Slug Head the unconformity between the Cowie Formation at the base of the Old Red Sandstone and the Highland Border Complex can be seen, but it is difficult to follow in detail. The Old Red Sandstone rocks form a series of pinnacles and crags striking out to sea and dipping south at about 70°. The contact between them and the underlying volcanics lies at the base of the pinnacles and in the cliff behind. The volcanics have an apparent dip to the north-west, but this is probably due to shear planes parallel to the plane of the main Highland Boundary Fault which lies about 100 m to the northwest. Poorly developed pillows are to be seen in a small bay north of that in which the unconformity occurs. They have been affected by shearing adjacent to the Highland Boundary Fault. Near LWM better pillows up to 1 m long are displayed and have clear outlines (Trewin ''et al.'' 1987, p. 272). They should not be hammered. More commonly the lava is crushed and sheared and has largely been converted to chlorite schist, hence the term greenstone, often applied to the rock. The lavas are continuously exposed on the shore as far as Ruthery Head. Small wedges of black siliceous shales, red jasper and chert also occur, along with stringers of the fault rock described below.

== 14. Ruthery Head: Highland Boundary Fault ==

On the north side of Ruthery Head the fault rock crops out on the beach among lava blocks and boulders. It is a dolomitic and siliceous carbonate, yellow-buff in colour both in fresh and weathered specimens and has a streaky appearance. It is cut by numerous carbonate veins and is believed to be a highly altered serpentine now lying in the line of the fault.

Exposures of the fault rock, the volcanics and the associated shales are much better on the north-east side of Craigeven Bay, the large mass of fault rock there being clearly visible from the south-west side. It is 12 m thick, has a sharp 70° north-west-dipping contact with the Dalradian rocks, but a rather diffuse contact with the rocks of the Highland Border Complex on its south-east side.

== 15. Craigeven Bay, north-east side: Highland Border Complex ==

Walk round Craigeven Bay, crossing over Dalradian grits and phyllites of the Southern Highland Group, to the north-east side and cross the thick fault rock. In the small bay 30 m to the south-east the strata dip north-west at about 70°, the cleavage and bedding being coincident. Black shales, some of them pyritous and cherty, can be seen interbedded with the volcanics. Individual beds of shale are up to 60 cm thick. Similar beds nearby have yielded inarticulate brachiopods and other fossils indicating an Ordovician age for the shales and associated volcanics (Curry ''et al.'' 1984).

== 16. Garron Point: Highland Border Complex rocks ==

Further exposures of the volcanics, in a schistose condition and cut by carbonate veins, can be seen by returning to Craigeven Bay and climbing up past an old coastguard but to Garron Point. Many stringers and veins of carbonate cut the volcanics. To the north-west on the Skatie Shore Dalradian rocks are well exposed. A detailed account of these and the section to the north can be obtained in Trewin ''et al.'' (1987).

Return to the road by walking 450 m north along the Skatie Shore to the Den of Cowie, a prominent dry valley spanned by a railway viaduct. Walk up this valley and continue to the road by a footpath which passes under the most northerly arch of the viaduct. The lay-by is 200 m to the south-west towards Stonehaven. The dry valley, occupied by the road, is a glacial overflow channel leading in from the sea at 55 m and running out again to the north at 30 m OD. According to Bremner (1925, p. 36) it was cut by melt water from the sea ice during the retreat of the last major Quaternary ice sheet.

Return to St Andrews by driving back down into Stonehaven; from the lay-by there is no access to the A90 to the north. From Stonehaven take the A90 to Dundee.

== References ==

ARMSTRONG, M. and PATERSON, I.B., 1970. The Lower Old Red Sandstone of the Strathmore Region. ''Rep. Inst. Geol. Sci. No. 70/12''

ARMSTRONG M., PATERSON, I.B., and BROWNE, M.A.E., 1985. Geology of the Perth and Dundee district. ''Mem. Br. Geol. Surv.'' Sheets 48W, 48E, 49.

BREMNER, A., 1925. The glacial geology of the Stonehaven district. ''Trans. Edinb. Geol. Soc. 11,'' 25–41.

CAMPBELL, R., 1913. The geology of southeastern Kincardineshire. ''Trans. Roy. Soc. Edinb.'' 48, 923–60.

CURRY, G.B. ''et al.,'' 1984. Age, evolution and tectonic history of the Highland Border Complex, Scotland. ''Trans. Roy. Soc. Edinb.: Earth Sciences'' 75, 113–33.

FRIEND, P.F. and WILLIAMS B.P.J., 1978. A ''field guide to selected outcrop areas of the Devonian of Scotland, the Welsh Borderland and South Wales.'' Palaeont. Assoc. International Symposium on the Devonian system.

HAUGHTON, P.W.D., 1988. A cryptic Caledonian flysch terrane in Scotland. ''Jour. Geol. Soc. Lond.'' 145, 685–703.

HENDERSON, W.G. and ROBERTSON, A.H.F., 1982. The Highland Border rocks and their relation to marginal basin development in the Scottish Caledonides. ''Jour. Geol. Soc. Lond.'' 139, 433–50.

RAMOS, A. and FRIEND, P.F., 1982. Upper Old Red Sandstone sedimentation near the unconformity at Arbroath. ''Scot. Jour. Geol.'' 18, 297–315.

TREWIN, N.H., KNELLER, B.C. and GILLEN, C. (Eds.), 1987. ''Excursion guide to the geology of the Aberdeen area.'' Scottish Academic Press, Edinburgh.

{{EGwalks}}
[[Category:4. Grampian Highlands]]
[[Category:5. Midland Valley of Scotland]]

File:P002860.jpg

2019-06-26T10:35:30Z

JamesMartin: JamesMartin uploaded a new version of File:P002860.jpg

== Summary ==
Whiting Ness, Arbroath, Angus. Unconformity of Upper Devonian upon Lower Devonian (Upper Old Red Sandstone and Lower Old Red Sandstone).

Whiting Ness, Arbroath, Angus. Unconformity of Upper Devonian upon Lower Devonian (Upper Old Red Sandstone and Lower Old Red Sandstone). Unconformity of the shallowly-dipping (c.10 degrees to the east-south-east) Upper Devonian red conglomerate and sandstone upon more steeply inclined (15 to 20 degrees to the south-east) red sandstones of the Lower Devonian strata (Arbroath Sandstone of the Garvock Group). A small fault shifts the unconformity on the right of the section. The unconformity can be traced for 250 m.

Photographer McTaggart, F.I.

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2019-06-26T10:18:27Z

JamesMartin: Whiting Ness, Arbroath, Angus. Unconformity of Upper Devonian upon Lower Devonian (Upper Old Red Sandstone and Lower Old Red Sandstone). Whiting Ness, Arbroath, Angus. Unconformity of Upper Devonian upon Lower Devonian (Upper Old Red Sandstone and Lo...

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