South Queensferry-Cramond, South Queensferry Shore - an excursion
By A.D. McAdam. 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
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.
- Paraffin Young Heritage Trail - starting at Grangemouth
- South Queensferry Shore
- Cramond shore
- Almond Valley
While the sections are seen best when the tide is low, most exposures on the coastal excursions are near High Water Mark (HWM).
South Queensferry Shore
The shore section exposes westerly dipping sediments of the Upper and Lower Oil-Shale groups, including oil-shales, limestones and marine and non-marine shell beds. Sills of white trap cut the sediments while further east are the Mons Hill teschenite sill and the Hound Point quartz-dolerite sill. The excursion starts at the Hawes Pier opposite the Hawes Inn (featured in R. L. Stevenson's Kidnapped).
1. Hawes Pier: Dunnet Sandstone
The pier and the south end of the Forth Railway Bridge (opened 1889) are built on the 90 m thick Dunnet Sandstone. Best seen just east of the bridge, the beds consist of pale brown and brown, fine to medium-grained, massive and cross-bedded deltaic sandstones. Layers in the sandstone contain ochreous plant stems and debris. U-shaped burrows near the top indicate local marine inundation. Sand-filled Stigmaria, hair-roots, sun-cracks and worm tracks show periodic exposure to air and establishment of forests. The steep dip of the basal sandstones is associated with faulting.
2. Port Neuk: Camps Shale, Burdiehouse Limestone
East of the sandstone outcrop poor exposures of the dark fissile Camps Shale and the hard grey Burdiehouse Limestone can be found among the shingle. The limestone has numerous ostracods, fish and plant fragments, and near L.W.M. it has been bored by modern molluscs.
3. East of Port Neuk: Sill, White Trap, Algal Limestone
The foreshore on the east of the bay is formed of thick brown and white fine to medium-grained deltaic sandstones showing various bedding structures. Near the top a brown-weathered pale grey altered dolerite sill, 90 cm thick, can be distinguished from the sandstone by polygonal jointing. Sun-cracks are prominent in the underlying dark baked sandstone near the sea-wall. In the cliff 40 m further cast is a striking outcrop of 'white trap', a sill of completely altered dolerite. The pale 60 cm thick sill, while generally concordant, also shows transgressive junctions with the dark hornfelsed sediments above and below. Thin dolerite sills intruded into carbonaceous mudstones, oil-shales or coals can become altered to white trap. The rock now consists mainly of carbonates of lime, magnesia and iron, kaolin and muscovite, but the original crystal structure of the dolerite can be seen in ordinary light under the microscope. Heat from the intrusion drove off from the carbonaceous beds by destructive distillation gases which altered the minerals in the dolerite.
A metre thick pale brown fine-grained ripple-bedded sandstone lies between the white trap and 1·1 m of thin finely laminated lagoonal cementstones which crop out round the point. Prominent algal patches near the top have rounded upper surfaces and flat bases. Lower down a thin desiccation breccia indicates drying out. Minor thrust faults at the point have caused fracturing with slickensides in sandstones and cementstones, but folding in the mudstones.
4. West of Long Rib: Mudstones, Pumpherston Shale
Underlying the cementstones are 25 m of dominantly argillaceous strata well-exposed in cliffs and foreshore. A marine mudstone 8 m from the top contains the bivalve Naiadites obesus and the branchiopod Euestheria sp. near the base, just west of the small stream, the Pumpherston Shale, seams of economic oil-shale with thin ironstone ribs, forms three prominent reefs.
Oil-shales can be identified in the field by the following characteristics: a brown streak or brown colour when scratched instead of the grey of normal mudstones, a toughness and resistance to weathering, a leathery appearance, a wooden sound when hammered, and parings cut with a knife curl up and do not crumble. Oil-shales have been classed as plain, in which the bedding is regular, or curly, in which the bedding shows penecontemporaneous contortion.
5. Long Rib: Pumpherston Shell Bed, Queensferry Cements
East of the stream the Pumpherston Shell Bed occurs in strata locally with steep to vertical dips. The shell bed comprises a 50 cm soft dark mudstone with yellow sulphurous efflorescence on a 3 cm limestone, both parts of which can be traced towards L.W.M. The fauna, mostly pyritised in the mudstones, includes the bivalves Aviculopecten, Pernopecten, Pteronites, Sanguinolites, Schizodus and Streblopteria, small Lingula, the gastropod Euphemites, orthocone nautiloids and ostracods.
Below a further metre of dark mudstones, two cementstones, the Queensferry Cements, form Long Rib, a conspicuous ridge running out to sea. The upper bed is a 35 cm yellow-weathering oolitic cementstone. The intervening grey mudstone is a metre thick. The lower cementstone is 1·2 m thick, is brown-grey but weathers yellow, and has cavities, some filled with bitumen.
Mudstones below the Queensferry Cements contain further cementstones and thin oil-shales. A 15 cm bedded cementstone forming an overhang in the cliff has mudstone flakes and brown coprolites containing fish fragments. Contorted mudstone just above this band could indicate a bedding-plane fault. The oil-shales include the Dalmahoy Shale, the lowest named oil-shale in the West Lothian shale field. The strata are mostly obscured by shingle towards Long Craig Pier, which is built on hard brown fine-grained sandstones dipping westwards at 25°.
6. Whitehouse Bay: Metamorphosed Sediments
Shingle obscures most of the sediments in the bay. Near H.W.M. 300 m east of Long Craig Gate, and opposite the grey hut on the road, are outcrops of greenish and greyish indurated spotted mudstones. These gently dipping strata were baked by the underlying teschenite sill, but the contact is obscured.
7. Whitehouse Point: Mons Hill Teschenite Sill
Outcrops of a differentiated teschenite sill form a kilometre of rocky foreshore between Whitehouse Bay and Peatdraught Bay. Detailed petrographic descriptions of the sill are given by Flett (in Peach et al. 1910) and by Walker (1923), who recognised several zones or modifications in a sill over 100 m thick. Joints however indicate that the sill dips gently and undulates and suggest it is much thinner, so that some of the zones may be lateral equivalents. Seen in descending order the principal rock-types are:
- Dark medium-grained theralite, small kersutite needles, undulating top
- Surface, angular joints, black and pink segregation veins; fairly sharp unchilled junction.
- Compact mottled sub-ophitic teschenite, angular joints; sharp basal contact at Whitehouse Point.
- Coarse to very coarse-grained mottled augite-tesehenite, purple ophitic titanaugite crystals up to 15 cm x 1 cm, analcimised plagioclase,chlorite, pink segregation veins and druses with zeolites, rounded joints; forms main bulk of sill between Whitehouse Point and the next point to the east.
- Dark sub-ophitic augite-teschcnite, angular joints: supposed to lie beneath the main part of sill, but mainly lie above it.
- Pale medium-grained theralite, small kersutite needles.
- Coarse-grained hornblende-teschenite, nepheline absent; seen just east of small stack; sharp unchilled junction.
- Dark medium-grained augite·teschenite. Idiomorphic, titanaugite, crystals, angular joints; base ohscured by sand.
8. Hound Point: Quartz-dolerite Sill
Sand in Peatdraught Bay covers sediments between the Monds Hill Sill and the Hound Point Sill. On the coast the westerly-dipping Hound Point quartz-dolerite sill is 20 to 30 m thick but thickens inland. Fine-grained blue-grey dolerite near the sill top is exposed in reefs near L.W.M. The bulk of the sill is dark medium-grained, columnar-jointed quartz-dolerite. East of Hound Point dark indurated mudstone with plant remains and fish scales is intercalated in the lower part of the sill. The base is transgressive and the underlying sandstone baked and tilted.
The excursion can be completed by returning along the inland track, or by continuing eastwards for the excursion to Cramond.
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