Page:Popular Science Monthly Volume 44.djvu/805

From Wikisource
Jump to: navigation, search
This page needs to be proofread.


THE ICE AGE AND ITS WORK. j%7

far above the native rock. Thus, bowlders of the peculiar Fox- dale granite are found about fourteen hundred feet higher than the highest point where there is an outcrop of this rock.

The Scotch ice-sheet flowed outward on all sides, but on the east it was met by the southward extension of the great Scandi- navian ice-sheet. On the extreme north the meeting of these two ice-sheets resulted in a flow to the northwest which glaciated the Orkney Islands, while the Shetlands, much farther north, received the full impact of the Scandinavian ice alone, and are therefore glaciated from the northeast. The dividing line of the Scotch and Scandinavian ice-sheets was in the North Sea, not far from the east coast of Scotland ; but farther south, at Flamborough Head and Holderness, the latter impinged on our coast, bringing with it enormous quantities of Scandinavian rocks. Many years ago Prof. Sedgwick described the cliffs of bowlder clay at Holderness as containing " an incredible number of smooth round blocks of granite, gneiss, greenstone, mica slate, etc., resembling none of the rocks of England, but resembling specimens derived from various parts of the great Scandinavian chain." These are mixed, how- ever, with a number of British rocks from the north and west, in- dicating the meeting ground of the two conflicting ice-sheets. Similar blocks occur all along the coast as far as the cliffs of Cro- mer in Norfolk. Across the peninsula of Flamborough about two miles west of the lighthouse there is a moraine ridge contain- ing a few Scandinavian bowlders, but mainly composed of British rocks. These latter consist of numerous carboniferous rocks from the north and northwest, together with many of Shap granite a peculiar rock found only on Shap Fell in the eastern side of the Lake District, together with a few of Galloway granite. These facts, it will be seen, add further confirmation to the theory of great confluent ice-sheets indicated by the ice-markings upon the various groups of mountains, while it is hopelessly impos- sible to explain them on any theory of local glaciers, even with the aid of submergence and of floating ice.

The study of our British erratics has been assiduously pursued for many years past by a committee of the British Association ; and by means of a map showing the chief facts collected up to this date, kindly furnished me by Mr. Percy F. Kendal, secretary of the committee, I am able to give a brief sketch of the more im- portant of the phenomena, and their bearing on the extent and motion of the British ice-sheet. The general reader may be in- formed that great numbers of rocks are so local and so character- istic, often being confined to a very limited district or to a single mountain, that the origin of a considerable portion of the errat- ics can be ascertained with the greatest certainty.

Taking first the Shap granite, which has already been men-

�� �