"The hypothesis upon which the southern extension is founded--that
the bowlder-clays have been formed by ice melting on the land--is
open to this objection, that _no similar clays have been proved to
have been so formed_, either in the Arctic regions, where the
ice-sheet has retreated, or in the districts forsaken by the glaciers
in the Alps or Pyrenees, or in any other mountain-chain. . . .

The English bowlder-clays, as a whole, differ from

[1. "The Great Ice Age," pp. 70-72.]

{p. 19}

the _moraine profonde_ in their softness, and the large area which
they cover. Strata of bowlder-clay at all comparable to the great
clay mantle covering the lower grounds of Britain, north of the
Thames, are conspicuous by their absence from the glaciated regions
of Central Europe and the Pyrenees, which were not depressed beneath
the sea."

###

A RIVER ISSUING FROM A SWISS GLACIER.

Moreover, the Drift, especially the "till," lies in great continental
sheets of clay and gravel, of comparatively uniform thickness. The
glaciers could not form such sheets; they deposit their material in
long ridges called "terminal moraines."