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PART II.—PHYSICAL FEATURES.
Plate Scotland forms the northern portion of Great Britain and is be of later than Silurian age. Recently, however, the structure of WII. divided from England by the rivers Sark, Liddell, and Kershops | Sutherland has been investigated anew with minute care and the (an affluent of the Liddell), the Cheviot Hills, the river Tweed, and result is to show that the schists, believed to overlie the Silurian the liberties of Berwick. The mainlandlies between 58° 40' 30" (at strata conformably have been really pushed over them and consist Dunnet Head, Caithness) and 54° 38' N. lat. (Mull of Galloway) and in part of the Archæan gneiss. It has been ascertained that from 1° 45' 30" (Peterhead) and 6° 14' W, long. (Ardnamurchan Point, the mouth of Loch Erriboll on the north coast of Sutherland southArgyllshire). Including the islands, the extreme N. lat is 60° wards to the Isle of Skye, a distance of more than 100 miles, a gigantic 51°30' (Outsack, Shetland) and the extreme W. long. 8° 35' 30" | system of earth-movements has taken place, whereby the Silurian, (St Kilda). Its greatest length from north to south, from Durness | Cambrian, and Archæan, rocks have been crumpled, inverted, disin Sutherland to Burrow Head in Wigtownshire, is 272 miles, and located, and have pushed over each other. In some places the horithe greatest breadth from east to west, from Peterhead in Aber- |zontal displacement of these shifted masses has been not less than deenshire to Applecross in Ross-shire, is 155, while the narrowest | 10 miles. ... So intense has been the shearing of the rocks that their part, from Grangemouth in Stirlingshire to Bowling in Dumbarton- original structure has in many places been entirely destroyed. shiré, is only 363 miles wide. The total area in 1881, according to They have *. a new schistosity, which is in a general sense the ordnance survey, was 19,777,490 acres or 30,902 square miles, parallel with the bedding of the Silurian rocks to the west of the —the area of foreshore being 310,413 acres or 485 square miles, line of disturbance. Hence the apparent conformability of the of water 403,846 acres or 631 square miles, and of land-surface schists overlying these rocks. . The total thickness of recognizable 19,063,231 acres or 29,786 square miles. But of the water area Silurian strata is about 2000 feet. The rocks that overlie them to the acreage included under lakes and rivers respectively has not the east of the line of disturbance in Sutherland and Ross are fine been ascertained. flaggy schists, quite unlike any part of the Archaean gneiss and often GEOLOGY strangely suggestive of altered sandstones. What are their true
. . - age and history remains still to be determined. There can be no
In the article Geology (vol. x.) descriptions will be found of most doubt, however, that they have acquired their present schistosity of the geological formations of Scotland. All that need therefore | since the Lower Silurian period, ol hence that the present condibe inserted here is a succinct summary of these formations with |tion of the metamorphic rocks of the central Highlands does not references to the pages of that article where fuller details are given. go back to Archaean time. That portions of the Archaean series Archaean The oldest rocks of Scotland and of the British Islands, known may have been pushed up in different parts of the Highlands is rocks. as Archaean, consist chiefly of gneiss (Fundamental, Lewisian, quite conceivable. But that much of the Highlands consists of
Hebridian), which varies from a coarsely crystalline granitoid mass
altered sedimentary rocks like those of the Silurian uplands admits
areas, particularly on the mainland, the bands of gneiss have a
As Scotland is the typical European Tegion for the Old Red Old Red: Sandstone a full account of this series of rocks has already been Sandgiven in the article GEOLOGY (vol. x. pp. 343, 344). These rocks stone.
tract of Archaean rock is that which forms almost the whole of the
prominent pyramidal mountains, which, as the stratification is.
usually almost horizontal, present in their terraced sides a singular
are grouped in two divisions, Lower and Upper, both of which appear to have been deposited in lakes. The Lower, with its abundant intercalated lavas and tuffs, extends continuously as a broad belt along the northern margin of the midland valley, reappears in detached tracts along the southern border, is found again on the south side of the uplands in Berwickshire and the Cheviot Hills, occupies a tract of Lorne in Argyllshire, and on the north side of the Highlands underlies most of the low ground on both sides of the Moray Firth, stretches across Caithness and through nearly the whole of the Orkney Islands, and is prolonged into Shetland. The Upper Old Red Sandstone covers a more restricted space in most of the areas just mentioned, its chief development being on the flanks of the north-eastern part of the southern uplands, where it spreads out over the Lammermuir Hills and the o of Berwick
-shire and Roxburghshire.
skirting the southern , uplands from the mouth of the Tweed to
Rocks assignable to the Permian system occupy only a few small Permian
areas in Scotland. Extending from Cumberland under the Solway Firth, they fill up the valley of the Nith for a few miles north of Dunfries, and, reappearing again in the same valley a little farther north, run up the narrow valley of the Carron Water to the Lowther Hills. Other detached tracts of similar rocks cover a considerable space in Annandale, one of them ascending the deep defile at the head of that valley. . Another isolated patch occurs among the Lead Hills; and lastly, a considerable space in the heart of the Ayrshire coal-field is occupied by Permian rocks. Throughout these separate basins the prevailing rock is a red sandstone, varied in the narrow valleys with intercalated masses of breccia (GEology, vol. x. p. 351). There can be no doubt that the valleys in which these patches of red rocks lie already existed in I’ermian time. They seem then to have been occupied by small lakes or inlets, not unlike fjords. Numerous amphibian tracks have been found in the red sandstone of Annandale and also near Dumfries, but no other traces of the life of the time. One of the most interesting features of the Scottish development of the Permian system is the occurrence of intercalated bands of contemporaneously erupted volcanic rocks in the Carron Water, Nithsdale, and Ayrshire. The actual vents which were the sites of the small volcanoes still remain distinct, and the erupted lavas form high ground in the middle of Ayrshire.
The Triassic system appears to be only feebly represented in Triassic.
Scotland. To this division of the geological record are assigned/ the yellow sandstones of Elgin, which have yielded remains of rep