South Queensferry-Cramond, Cramond shore - an excursion

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By G. Robertson. From: Lothian geology: an excursion guide. Edited by A.D. McAdam and E.N.K. Clarkson. 1996


O.S. 1:50000 Sheet 65 Falkirk and West Lothian

B.G.S. 1:50000 Sheet 32W Livingston

Introduction[edit]

THE object of this group of excursions is to study the Dinantian oil-shale bearing sediments of West Lothian, as exposed along the coast from South Oueensferry to Cramond, and to look at relics of the vast industry based on exploitation of the oil-shale. Also well displayed are teschenite sills of Namurian age and quartz-dolerite sills of Stephanian age, and their intrusive relationships to the sediments.

The area lies near the centre of the basin in which the oil-shale bearing beds were deposited. The basin was open to the north-cast, from which direction sediment was derived, and cut off by Lower Palaeozoic rocks of the Southern Uplands to the south-east. In other directions it was enclosed by volcanic piles. In the cyclical sediments the lagoonal oil-shales are underlain by marine or freshwater limestones and mudstones and succeeded by thick mudstone-siltstone-sandstone sequences of f1uvio-deltaic origin. Coals are rarely developed. The strata are divided into the Lower and the Upper Oil-Shale groups (Carruthers et al. 1927). the boundary being taken at the base of the freshwater Burdiehouse Limestone. The rocks belong to the Asbian and Brigantian Stages of the Visean. The main marine marker band is the lowest widespread marine horizon in the local Carboniferous, the Pumpherston Shell Bed. It is found throughout West Lothian and is recognised in Midlothian and East Lothian as the Macgregor Marine Bands and Cove Marine Bands (Wilson 1974). Beds below and including the Pumpherston Shell Bed belong to the TC miospore zone, higher beds to the NM zone.

Four half-day excursions are listed, which can be combined to make one or two day excursions.

While the sections are seen best when the tide is low, most exposures on the coastal excursions are near High Water Mark (HWM).

Cramond Shore[edit]

Along this stretch of coast the interest includes sedimentary sequences and structures, intrusions and their contacts, raised beaches and the buried channel of the River Almond. This excursion follows on from Excursion B, or can be reached by crossing the Cramond Ferry and taking the path to Snab Point, Barnbougle Castle or Hound Point.

9. Barnbougle Castle, Dalmeny House: Raised Beach, Buried Channel[edit]

Westward-dipping brown fine-grained sandstones crop out at H.W.M. 800 m east of Hound Point and at Barnbougle Castle. The Buchans, reefs near L.W.M. are formed of green and purple amygdaloidal columnar basalt lava and red, brown and grey sandstone. The post-Glacial raised beach with its well-defined back-feature is narrow as far as Barnbougle Castle and widens out in front of Dalmeny House. This magnificent Tudor-Gothic style house was built in 1815 by William Wilkins for the Earl of Roseberry. It con­tains the Roseberry and Mentmore collections and is open during afternoons in summer. The statue is the horse King Tom. Low ground south-east of the house lies along the pre-glacial channel of the River Almond blocked by glacial deposits.

10. Snab Point: Quartz-dolerite Sill, Sedimentary Sequence[edit]

Leaving the low raised beach, the path climbs sharply up the dip slope of the Snab Point quartz-dolerite sill. The top of the sill forms a dramatic slope of hard, black well-jointed dolerite dipping WNW at 25° into the sea. Just east of Snab Point the basal contact of the sill against baked mudstones is exposed at H.W.M.

Starting 200 m east of the sill is a cliff section of sedimentary rocks, dipping westwards at 15°. The highest 3 m comprises thin brown sandstones overlying grey mudstones and siltstones with plant fragments and irony ribs and nodules. Below these a 15 cm coal seam is underlain by 5 cm of grey seatclay. Most of the section is formed of a massive brown sandstone. 8·5 cm thick, showing large-scale cross-bedding. Loose blocks have fine rippled surfaces. The lowest 9 m of the section consists of grey siltstones with bands of pale brown sandstone.

11. Eagle Rock or Hunter's Craig: Sandstone[edit]

As well as the historical interest, for the defaced figure of an eagle carved on the rock is supposed to be of Roman origin, the stack demonstrates sedimentary structures of a fluvio-deltaic sandstone. The main face shows 3·6 m of laminar sandstone on 1·8 m of cross-bedded sandstone with an irregular 5 cm irony rib along the junction. On the seaward side are ancient ripples similar to modern ripples in the beach sand. Another rock further west shows 3 m of slumped contorted sandstone on 1·8 m of laminar and cross-bedded sandstone.

12. Cat's Craig: Teschenite Sill[edit]

Looking at first like an old stone wall the craig is the outcrop of the thin upper leaf of a teschenite sill. During post-Glacial raised beach times the craig formed an intertidal reef.

13. Coble Cottage: Teschenite Sill[edit]

The ferry house and jetty stand on a cliff formed by the lower leaf of the teschenite sill, the same rock-type that forms Cramond Island offshore. Coble Cottage sits on the middle of three raised beaches on the west side of the River Almond. Cross the river by the ferry and visit Cramond Heritage Trail Centre.

At all times follow: The Scottish Access Codeand Code of conduct for geological field work