Ragnarok : the age of fire and gravel

CAUSED BY CONTINENTAL ICE-SHEETS? 31

And, even in North America, the Drift is not found everywhere. There is a remarkable region, embracing a large area in Wisconsin, Iowa, and Minnesota, which Professor J. D. Whitney* calls “the driftless region,” in which no drift, no clays, no gravel, no rock striz or furrows are found. The rock-surfaces have not been ground down and polished. “ This is the more remarkable,” says Geikie, “seeing that the regions to the north, west, east, and south are all more or less deeply covered with driftdeposits.” And, in this region, as in Siberia, the remains of the large, extinct mammalia are found imbedded in the surface-wash, or in cracks or crevices of the limestone.

If the Drift of North America was due to the ice-sheet, why is there no drift-deposit in “ the driftless region” of the Northwestern States of America? Surely this region must haye been as cold as Illinois, Ohio, ete. It is now the coldest part of the Union. Why should the ice have left this oasis, and refused to form on it? Or why, if it did form on it, did it refuse to tear up the rock-surfaces and form Drift ?

Again, no traces of northern drift are found in California, which is surrounded by high mountains, in some of which fragments of glaciers are found even to this day.f

According to Foster, the Drift did not extend to Oregon ; and, in the opinion of some, it does not reach much beyond the western boundary of Iowa.

Nor can it be supposed that the driftless regions of Siberia, Northwestern America, and the Pacific coast are due to the absence of ice upon them during the Glacial

* “Report of the Geological Survey of Wisconsin,” vol. i, p. 114.

+ “The Great Ice Ave,” p. 465.

¢ Whitney, “Proceedings of the California Academy of Natural Sciences,”