Scotland

Carboniferous.

The Scottish Carboniferous, a marine, estuarine and terrestrial accumulation, is typically developed in the Central Valley and along the English Borders. The two areas of deposition were always connected across the east end of the southern Uplands. Farther west (Sanquhar) Upper Carboniferous rests on Silurian. In the Highlands, Carboniferous is scarcely known (Campbeltown, Bridge of Awe, Morven). In the Central Valley and on the Borders, it follows Upper Old Red Sandstone conformably, though with a palaeontological break. Measurements of sub-divisions in Edinburgh district are: Calciferous Sandstone Series, including Cementstone Group (i,000 ft.) and Oil Shale Group (3,000 ft.) ; Scottish Carboniferous Limestone Series, in cluding Lower Limestone Group (70o ft.), Limestone (or Edge) Coal Group ( i,o5o ft.), and Upper Limestone Group (i,o5o ft.) ; Millstone Grit (800 ft.) ; Productive Coal Measures (1,50o ft.) ; Barren Red Coal Measures (in Ayrshire, 1,500 ft.). Palaeonto logically, the sequence is important for its abundant Lower Car boniferous land plants and estuarine fishes. These are completely replaced by English Upper Carboniferous forms one-third way up the Millstone Grit.

Economically, the oil shale and the two widely separated coal bearing groups (with ironstones) are very valuable. Marine lime stones are scarcely represented except in the Lower and Upper Limestone Groups (near Edinburgh, 8 beds reach the quite ex ceptional total of 23o ft.). A well-known 4o-ft. fresh-water lime stone (Burdiehouse) occurs in the Oil Shale Group. Rapid varia tions of group-thicknesses are characteristic. Near Patna in Ayr shire, the Lower Limestone Group reduces from 7o ft. to 3o ft., the Limestone Coal Group from 26o ft. to ioo ft., the Upper Lime stone Group from 700 ft. to 4o ft., and the Millstone Grit from 390 ft. to 120 ft. in a distance of 2 miles. The floor of deposition evi dently subsided in independently moving blocks. Change of facies is exemplified by the restriction of workable oil shale to West Loth ian and its borders. Vulcanicity is common till the close of the Mill stone Grit. Special activity reigned about the end of the Cement stone Group (Clyde Plateau, Arthur's Seat, Calton Hill). Prod ucts include essexitic basalts, mugearites, trachytes and phono lites. Contemporaneous weathering of Millstone Grit basalts has given valuable bauxitic clay (Ayrshire).

New Red Sandstone.

The Scottish deposits are of conti nental facies. A train of outcrops reaches intermittently across the southern Uplands and Central Valley from the Solway to Arran. In Ayrshire, lavas and tuffs (basalt and nepheline-basalt, 50o ft.) underlie brick-red desert sandstone (1,50o ft.). The vol canic period was one of faulting and was further marked by ash necks and doleritic intrusions, some (essexitic) carrying nepheline, others quartz. It may correspond roughly with the

Permo-Carboniferous intrusion period of many quartz-dolerite sills and east to west dykes between Stirling and Northumberland. In Arran brick-red desert-sandstone (2,00o ft.) underlies breccia, sandstone, and interbedded sandstone and marl with occasional nodular limestone. The top division, probably Keuper, is over lain, in a fallen mass within a Tertiary volcanic neck, by Pteria contorta shales (Rhaetic).

The base of the Mesozoics from Mull northwards consists of Trias conglomerates and sandstones with concretionary corn stones. Red colouration is often subordinate. In Western Mull 200 ft. of these rocks underlie 4o ft. Rhaetic with Pteria contorta. Elsewhere Rhaetic is only doubtfully distinguishable.

In Elgin two outliers of New Red Sandstone have yielded remarkable reptilian faunas. One of these outliers is of marked desert character and perhaps of Permian age, the other outlier is certainly Trias.

Jurassic.—Low-lying outcrops of Jurassic, conformable to Trias, are preserved on the west and east coasts of the Highlands. On the west, where a cover of Tertiary lavas has furnished addi tional protection, the type area is Skye and Raasay : Lower Lias (Broadford Beds, mostly limestone, 24o ft.; Pabba Shales, 600 ft.) ; Middle Lias (Scalpa Sandstone, 240 ft.) ; Upper Lias (shales, 7o ft.; Raasay Ironstone, 8 ft.) ; Inferior Oolite (shales, 7o ft.; sandstone, 600 ft.) ; Great Estuarine Series (sandstone, bitumi nous shale and limestone, 400 ft.) ; Cornbrash (limestone with comminuted fossils, only in Raasay, 20 ft.); Callovian (sandstone remnant in Skye) ; Upper Oxfordian (grits, Skye, 8o ft.) followed by Upper Oxfordian and Corallian (shales, Skye, 220 ft.). The sequence also reaches Corallian in Eigg, but in Ardnamurchan and Mull ends with Inferior Oolite. The Hebridean marine faunas are as rich as any in Britain. The Great Estuarine Series, agreeing in age with the Yorkshire Upper Estuarine Series, contains Cyrena, Viviparus, Ostrea, etc.

At Brora on the east coast are remarked : Lower Lias (shales, 8o ft.) ; Great Estuarine Series (over 8o ft. shale, sandstone, etc., with 3 ft. Brora Coal at top) ; Callovian (limestone, 5 ft.) ; Lower Oxfordian (shales, 275 ft.) ; Upper Oxfordian and Corallian (sand stone, 200 ft.); Kimmeridgian (sandstone and bituminous shale, zoo ft.; boulder-beds and shales, 500 ft.). The boulders of the boulder-beds consist of Old Red Sandstone. Many are big; one measures i 5o X 90 X 30 ft. They have fallen from a moving submarine fault-scarp and are mixed with corals and shells. The throw of the fault exceeds 2,000 ft. In Skye another 2,000 ft. post-Corallian fault can be shown to have been planed down by erosion before Upper Cretaceous times.