The Striation of Stones in Boulder Clay

Abstract

IN NATURE of September 5, Dr. A. Irving, in criticism of statements by Mr. Reid Moir, asks “how could the soft matrix of the Boulder Clay scratch a flint, or even hold a harder stone with sufficient grip to give it effect as a graving-tool?” It is true that one may see flints emerging from arctic glaciers unscratched and unrounded, while softer rocks are reduced to strongly striated boulders; but Dr. Irving seems to conceive the Boulder Clay as something distinct from the ice-sheet in which it originated, and as merely pressed on by superincumbent ice. It cannot be too strongly urged that the lower portions of glaciers ot the continental or ice-sheet type consist largely of stones and mud and abrading sand-grains, and that these materials are held in the grip of the ice and are moved against one another as it flows. The ice-sheet is, in fact, a conglomerate with an ice cement; the Boulder Clay is an essential part of it, and remains as its representative when the portion that can melt has yielded before climatic change.