File:Geological sketches, at home and abroad (1882) (14779430931).jpg

Identifier: geologicalsketch00geik (find matches)
Title: Geological sketches, at home and abroad
Year: 1882 (1880s)
Authors: Geikie, Archibald, Sir, 1835-1924
Subjects: Geology
Publisher: New York : Macmillan and Co.
Contributing Library: Harold B. Lee Library
Digitizing Sponsor: Brigham Young University

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ormations, would be the last to be attacked, and inso far as it was so covered, must have been exposed to theerosive action of the ice for a shorter time than the over-lying rocks. We might therefore have presumed that insteadof being more, it would have been less trenchantly worndown than these. Its great toughness and durability, whichhave enabled it to retain the ice-impress so faithfully, musthave given it considerable powers of resistance to the grind-ing action of the glacier. Every fresh excursion into these northern wilds has in-creased my difficulty in accounting for the peculiar contoursof the gneiss ground by reference merely to the work of theGlacial Period. A recent visit, however, seems at last tohave thrown some light on the matter. I had long beenfamiliar with the fact that the platform of gneiss on whichthe red sandstones and conglomerates were laid downabounded in inequalities even at the time of the deposit ofthese strata. Its uneven surface rose here and there into
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i56 GEOLOGICAL SKETCHES. (vii high ridges and cones, of which Stack is a diminishedrepresentative, and sank into depressions now occupied bythick masses of sandstone. But I have lately observed thatnot only do these larger features pass under the sandstone,but that the minor domes and bosses of gneiss do so like-wise. On both sides of Loch Torridon, for example, thehummocky outlines of the gneiss can be seen emergingfrom under the overlying sandstones (Fig. 21). On theside west of Loch Assynt similar junctions are visible. Butsome of the most impressive sections occur in the neigbour-hood of Gairloch. Little more than a mile to the north ofthe church the road to Poolewe descends into a short valleysurrounded with gneiss hills. From the top of the descentthe eye is at once arrested by a flat-topped hill standing inthe middle of the valley at its upper end, and suggestingsome kind of fortification : so different from the surround-ing hummocky declivities of gneiss is its level grassy to

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