414 SUMMARY OF WORK. 



the gradual erosion of the valleys is marshalled with 

 great skill, and discussed with characteristic clearness 

 and caution. In later essays he admitted that man 

 was living in Glacial or Post- Glacial times which came 

 down approximately to within 10,000 or 12,000 years 

 of our own day [116, 122]. 



Thus it is to Prestwich, more than to any other 

 geologist, that we owe the establishment of the fact 

 that man coexisted with a number of now long extinct 

 mammals, and that his advent on the earth must be 

 relegated to a far higher antiquity than that which 

 had previously been accepted. While he was engaged 

 in the researches that led to these results, he at the 

 same time greatly enlarged our knowledge of the later 

 phases of the Ice Age, particularly in the river-valleys 

 of the south of England and north-west of France. 

 The term " Drift " has been vaguely applied to a mul- 

 tifarious series of superficial deposits, differing widely 

 from each other in origin and in age. Prestwich 

 strenuously contended for the local origin of the 

 gravels in which flint-implements and mammalian re- 

 mains occur together. He showed that these accumu- 

 lations unquestionably belong to the river - systems 

 within which they are found, that they were fluviatile 

 in origin, and were deposited by the streams which 

 still flow in the same valleys. He maintained, how- 

 ever, that the rivers were formerly vastly larger than 

 they are now ; that, in virtue of their size, width, and 

 transporting power, they were able to carry downward 

 and spread out over their flood-plains the widely dis- 

 tributed sheets of coarse shingle now remaining ; while 

 from time to time they rose in floods of extraordinary 

 magnitude that deposited the fine silt, containing land- 

 shells, which is now to be seen covering all the differ- 



