190 
THE OEOLOGIST. 
not exceeded twenty-nine feet, but it would require the present rivers to 
be of a hundred times that volume to fill the existing valley. That the 
terraces were originally connected is proved by the isolated patches of 
their gravels still' lying at elevated spots between them. The author 
believed that the gravels were brought and distributed by ice and by the 
melting of the winter snows in spring pouring down great bodies of water, 
the gravels enclosing boulders of hard rock, brought often from long dis- 
tances. He also attributed much importance to the action of ground ice. 
He pointed out contortions in the drift-bed at St. Acheul, as formed by 
the pressure and squeezing force of massive ice. The characters of the 
gravels were then considered, in reference to the climatal condition of the 
drift period, which the author argued were those of a more intense cold, 
by 20° or 25°, than the average of our present winters. The bearings of 
the geographical distribution of the animals of that period, and its com- 
parison with those of existing forms of life, were also assumed to confirm 
this inference. The use assigned for some of the largest flint implements 
was that of making holes in the ice. — the men of the drift-age, like the 
JS^orth.- American Indians and the Esquimaux, being very often depen- 
dent upon winter supplies of fish. Since the formation of the high- 
l"vel gravels, an elevation of the land has taken place, and the present 
valleys excavated, and the lower gravels deposited. The tendency of 
existing rivers was to cut deep gorges, and not valleys, with sloping sides, 
such as those containing the gravels. The large flint implements were no- 
where so abundant in the valleys as in the terrace-gravels. Flint-flakes, 
on the contrary, were most common in the valley-gravels, — the climate of 
the valley-period being more lenient, there was a diminished need of great 
flint chisels for breaking the ice. These distributions, at two periods, of 
different forms of implements indicated a difference in the habits of the 
tribes by whom they were respectively used. 
In the questions of time and succession the value of probabilities must 
be considered. The antiquity of the flints was carried back through three 
geological ages, — the loess, terrace, and valley-gravels ; all long periods 
except the loess, the duration of which was comparatively short. The 
saiid-pipes in the valley of the Somme were first considered as a standard 
of time-measurement ; and then the author commented upon the probable 
condition, at those periods, of the British Channel, the formation of which, 
while a late geological event, he was not prepared to admit to be one of 
the last. Even in the Pleistocene period the British Channel existed, 
although much narrower, and there was a line of cliffs running parallel 
witli the present coasts. The sea being narrower, was frozen over every 
winter, permitting the passage of men and animals. Some of the great 
effects of such a cold period might already be conceived, although it might 
not be in our power as yet to accurately define them. In looking at a 
distant mountain-chain we could judge of its great magnitude without 
waiting for a trigonometrical survey to be assured of its exact dimensions. 
The author then suggested as a possible measure of time the perturbations 
in the increasement of heat at various depths in the earth's crust, arising 
from disturbances originating with the glacial period ; and he concluded 
by giving his impression that in the existence of this remarkable cold 
period preceding our own, we might possibly trace evidence of great and 
allwise design by the circumstance that, in this long glacial era. the earth's 
crust would tend to acquire an earlier adjustment in its equilibrium, and 
obtain a rigidity and stability which should make it more fitting for the 
habitation and pursuits of civilized man. 
