PLEISTOCENE RIVER-DEPOSITS. 133 



up the valley-slopes so as to cap the summits of hills far above 

 the level reached by the highest river-gravels, proves the for- 

 mer existence of floods, as Professor Prestwich has pointed out, 

 of extraordinary magnitude. The same geologist has described 

 the occurrence in the valley-gravels of large transported boul- 

 ders or erratics, some weighing as much as four to five tons, 

 which have been often carried for considerable distances ; and 

 besides these he records many examples of contorted or con- 

 fused bedding which seem to be confined to the higher gravels 

 and loams. The erratics, he believes, have been transported by 

 river-ice, and the disturbed bedding he ascribes to the action of 

 masses of the ice running aground, and digging into the soft 

 deposits upon the river's bed. The fact that the river-ice was 

 so thick as to be capable of carrying blocks of stone weighing 

 several tons renders it more than probable that in Pleistocene 

 times the winter temperature was sometimes at least severe. 

 And this inference, Mr. Prestwich thinks, is further borne out 

 by the character of the fossils met with in the old river-deposits. 

 Thus in regard to the high-level drifts he is of opinion that 

 although the shells which they have yielded have " nothing suf- 

 ficiently specific in the individual species to indicate a climate 

 different from that of the present day, there is at the same time 

 nothing to require restriction to an identical climate. If, 

 further," he continues, " we look at the group as a whole, we 

 shall find it to have not only a very wide range, but one more 

 in a northern than in a southern direction." The few plant 

 remains which have been met with in these higher beds afford 

 somewhat similar evidence — they all belong to species which, 

 although common in our latitudes, have yet a considerable 

 northern range, and there appears to be an absence of southern 

 forms. The evidence supplied by the mammalian relics (which 

 include remains of the mammoth, Elephas antiquus, the woolly 

 rhinoceros, the horse, the urus, the reindeer, etc.) does not seem, 

 according to the same authority, to militate against that fur- 

 nished by the testacea and the land-plants. All the recent 

 species of molluscs and plants " are such as are now to be found 



