This hypothesis explains the carriage of enormous blocks weighing hundreds of tons from their original site to where they are now found; but it is open to many unanswerable objections.
In the first place, if the Drift had been deposited under water deep enough to float icebergs, it would present throughout unquestionable evidences of stratification, for the reason that the larger masses of stone would fall more rapidly than the smaller, and would be found at the bottom of the deposit. If, for instance, you were to go to the top of a shot-tower, filled with water, and let loose at the same moment a quantity of cannon-balls, musket-balls, pistol-balls, duck-shot, reed-bird shot, and fine sand, all mixed together, the cannon-balls would reach the bottom first, and the other missiles in the order of their size; and the deposit at the bottom would be found to be regularly stratified, with the sand and the finest shot on top. But nothing of this kind is found in the Drift, especially in the “till”; clay, sand, gravel, stones,
and bowlders are all found mixed together in the utmost confusion, “higgledy-piggledy, pell-mell.”
“Neither can till owe its origin to icebergs. If it had been distributed over the sea-bottom, it would assuredly have shown some 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."
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."
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?
[1. “The Great Ice Age,” p. 72.
2. “American Cyclopædia,” vol. vi, p. 112.]