kind of arrangement. When an iceberg drops its rubbish, it stands to
reason that the heavier blocks will reach the bottom first, then the
smaller stones, and lastly the finer ingredients. There is no such
assortment visible, however, in the normal 'till,' but large and
small stones are scattered pretty equally through the clay, which,
moreover, is quite unstratified."[1]

This fact alone disposes of the iceberg theory as an explanation of
the Drift.

Again: whenever deposits are dropped in the sea, they fall uniformly
and cover the surface below with a regular sheet, conforming to the
inequalities of the ground, no thicker in one place than another. But
in the Drift this is not the case. The deposit is thicker in the
valleys and thinner on the hills, sometimes absent altogether on the
higher elevations.

"The true bowlder-clay is spread out over the region under
consideration as a somewhat widely extended and uniform sheet, yet it
may be said to fill up all small valleys and depressions, and to be
thin or absent on ridges or rising grounds."[2]

That is to say, it fell as a snow-storm falls, driven by high winds;
or as a semi-fluid mass might be supposed to fall, draining down from
the elevations and filling up the hollows.

Again: the same difficulty presents itself which we found in the case
of "the waves of transplantation." Where did the material of the
Drift come from? On what sea-shore, in what river-beds, was this
incalculable mass of clay, gravel, and stones found?