190 



THE GEOLOGIST. 



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 

 Korth- American Indians and the Esquimaux, being very often depen- 

 dent upon winter supplies of fish. Since the formation of the high- 

 level 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 

 sand-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, 

 wliile 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, 

 altliough much narrower, and there was a line of cliffs running parallel 

 with 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 autlior then snggested as a possible measure of time the perturbations 

 in the hu-reasement 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 

 ]ieriod jiroceiling our own, we might possibly trace evidence of great and 

 allw ise design by the circumstance that, in this long glacial era. tlie earth's 

 crust would lend to acquire an earlier adjustment in its equilibrium, and 

 obtain a rigidity and stability which should make it more fitting for the 

 liabitation and pursuits of civilized man. 



