The chief characteristic of the present stage of investigations of the Ice age and its glacial and modified drift deposits seems to consist in the search, through observations and study, for explanations of the methods in which the ice-sheets of North America, northern Europe, Patagonia, and other glaciated areas, acted in eroding, mingling, transporting and depositing the various drift formations.
All the diverse phases of the till or ground moraine, also called boulder-clay, from its heterogeneous materials, and including much englacial drift, which was allowed to fall loosely on the ground from the ice during its stages of retreat, are classed together as direct products of the action of land ice, without modification by the assorting, transporting and stratifying agency of streams and lakes formed by the glacial melting and accompanying rains. Most drumlins in their entire mass, and all others in their superficial part, consist of till, an . . .