South Queensferry-Cramond, Almond Valley - an excursion

From Earthwise
Jump to navigation Jump to search

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


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 fluvio-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 - excursion map

Almond Valley[edit]

This excursion follows along the pleasant riverside walks of the Cramond Heritage Trail. The geomorphology of the Almond valley can be studied as well as thick sandstones. complex sills and their contacts. The excursion starts at the Heritage Trail Centre, near the ferry landing point.

14. Cramond Heritage Trail Centre: Ravelston Sandstone, Raised Beaches[edit]

On the path outside the centre is a pale brown cross-bedded sandstone correlated with the Ravelston Sandstone. Two raised beaches east of the River Almond are evidence of higher sea-levels. The lower, post-Glacial, beach forms the terrace with a steep back slope on which the promenade stands. Material from the higher late-Glacial beach can be seen on the banks behind Cramond Boat Club, consisting of brown silty clay with pebbles, numerous oyster shells and a few Pecten and gastropod shells.

15. Quarries: Sill-sediment Relationships[edit]

Quarried cliffs above the path show two thin teschenite sills. the upper at least 3·5 m thick. the lower 1·8 m thick, dipping at 30° to north-west. The 60 em mudstone between the sills has a pale grey hard baked ceramic look and has been welded on top of the lower sill. Below the teschenite is a white rusty-mottled fine-grained sandstone over 8 m thick well exposed in a quarried face. Vertical drill holes at the north end are relics of the quarrying. At the weir the milllade has been cut into a further outcrop of teschenite.

16. Cockle Mill Weir: Hailes Sandstone, Faulting[edit]

Beyond the weir is a long 5 m high quarried face of sandstone dipping east. Note the change of dip from the previous outcrop, due to a fault just above the weir. The cliff of pale brown, part thinly bedded, part large-scale cross-bedded sandstone is broken up by two fault zones of disturbed rock. A prominent 30 cm dark purple band is hematite-stained sandstone.

17. Fairafar Iron Mill: Hailes Sandstone Gorge[edit]

At first sight looking as if built with red sandstone, this ruined mill was in fact built of a local pale brown sandstone. The red irony skin was formed during operation of the foundry, and stones on the weir are similarly affected. For the next 300 m the river flows through a gorge with steep sandstone walls 10 m high. The pale brown sandstone shows laminar and cross-bedding. It was exploited in Craigiemill Quarry across the river. Glacial till forms the tree-covered upper slopes of the valley. Exposures of the dark clay till, with pebbles such as sandstone, dolerite and vein quartz, can be seen at the top of the upstream steps. Beyond the gorge thicker glacial till forms gentler valley sides, upriver of Peggy's Mill.

18. Grotto Gorge: Mudstones, Quartz-dolerite Sill, Buried Channel[edit]

Cross to the north side of the river at Cramond Bridge and take the path to the left opposite Willowbank to rejoin the riverside walk. At the start of the rock gorge a cliff of bedded mudstones can be seen on the opposite bank dipping at 15° to the west under the Snab Point quartz-dolerite sill. A fine view from the bridge shows the gorge cut in jointed quartz-dolerite dipping west. The sill forms ridges north and south of the river. Upstream the open valley marks thick glacial deposits which blocked the former valley of the Almond and forced the river to cut the rock gorge. Return to the A90 at Cramond Bridge or all the way to Cramond.

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