Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/208

108 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Dec. 8, which I have been deducing from physical evidence; for though we do not find any one of the peculiar shells of Bridlington amongst them, all of them belong to existing forms, and one, the uddevallensis variety of Mya truncata, is unknown either to the Crag, to the Lower, or to the Middle Glacial, and is also unknown at Bridlington, while it occurs in the yet newer beds of the Clyde, and is still living.

Very unlike the Bridlington fauna also is that of Moel Tryfaen, given in detail by Mr. Darbishire*. The list from that place is moreover equally unlike that of the shells from the Middle and Lower Glacial and from the Crag. The Moel-Tryfaen fauna, however, must have lived when this country was depressed nearly as much below the present sea-level as it was when the Shap boulders came over into the purple clay; but we must recollect that equal degrees of depression do not necessarily, even if the movement were uniform, imply an identity in age between deposits accumulated under them, since the one deposit may have been formed when the land was going down, and the other when it was rising, and the two be thus separated by a not inconsiderable interval of time, during which material changes in temperature may have occurred. The Moel-Tryfaen bed therefore, instead of being synchronous with the purple clay without chalk, may not improbably belong to the epoch of emergence — that is to say, to the very earliest part of the Post-glacial period, that, in fact, to which Mr. A. Geikie refers the stratified drift of Scotland.

The prevalence of high land throughout Scotland, coupled with its higher latitude, concur to suggest that the ice-sheet would cling to that country after the far less elevated and more southern districts of the east and east centre of England had become freed from it; and the belief is therefore strong with me that the Glacial beds of Scotland belong, if not wholly, yet in greater part, to such later deposits as the north-of-England Glacial clay. One remarkable exception, however, exists to this, in the Aberdeenshire bed described by Mr. Jamieson in the 16th vol. of the Society's Journal (p. 347), which, both in its physical structure and organic contents, seems to agree with the Middle Glacial formation of England.

Note. — Since this paper was sent in with the lower representation of the triple section drawn to such a supposed submergence (1500 feet) as would cover Stainmoor Pass with sea, I have been enabled, by the kind assistance of Mr. Thos. M'K. Hughes (who is engaged on the geological survey of the district), to point out what other routes than that of Stainmoor Pass exist by which floating ice bearing Shap boulders could, so far as elevation is concerned, have passed the dividing ridge under such a submergence as represented. These routes are as follows: — 1. Up the valley of the Eden, and so over into the valley of the Ure, and thence into Wensleydale.


 * Geol. Mag. vol. ii. p. 298.