III. On the Origin of Certain Granite Boulders in the Clyde Valley

Abstract

More than fifty years ago, the late Mr. Smith of Jordanhilh—one of the founders of Glacial Geology—noted the occurrence of a certain number of granite boulders in the “Till” around Glasgow, and estimated their proportion as about 1 per cent, of the whole stony contents. About 60 per cent., he observed, were of sandstone and shale derived from the subjacent Carboniferous rocks; 30 per cent, were of trap from the Kilpatrick hills, about ten miles to the north-west; 9 or 10 per Cent, of clay-slate and “greywacke” from mountains in Dumbarton and Argyle shires, about twenty miles away in the same direction; while “the granite blocks must have been transported from still greater distances. Beyond the Kilpatrick hills,” he added, “the trap and white sandstone boulders disappear and are replaced by greywacke, clay-slate, and red sandstone, while those of granite and mica-slate become numerous,” and also increase in size. The inference was, therefore, in all respects well supported that “the cause which produced the diluvial covering of the great coal-field of Scotland must have had its origin to the westward.”* As to the exact locality from which these granite boulders had been brought, Mr. Smith at first thought of Inveraray for some, and even of Ardnamurchan for others; but ultimately seemed to prefer Ben Cruachan as the most likely source. Thus, finding a small granite boulder in the “Till” at Chapelhall, near Airdrie, he remarked that to the east and south of Glasgow such boulders are comparatively rare and small, This 250-word extract was created in the absence of an abstract