CLOSE OP POST-PLIOCENE — ADVENT OF MAN. 295 



wooded condition of the country, a greater rainfall, 

 and a glacial filling of the Somme valley with clay 

 and stones subsequently cut out by running water 

 the gravels could scarcely be older than the Abbeville 

 peat. To have published such views in England 

 would have been simply to have delivered myself 

 into the hands of the Philistines. I therefore con- 

 tented myself with recording my opinion in Canada. 

 Tylor * and Andrews f have, however, I think, 

 subsequently shown that my impressions were correct. ]^ 



In like manner, I fail to perceive, — and I think all 

 American geologists acquainted with the pre-historic 

 monuments of the western continent must agree with 

 me, — any evidence of great antiquity in the caves of 

 Belgium and England, the kitchen-middens of Den- 

 mark, the rock- shelters of France, the lake habita- 

 tions of Switzerland. At the same time, I would 

 disclaim all attempt to resolve their dates into precise 

 terms of years. I may merely add, that the elaborate 

 and careful observations of Dr. Andrews on the raised 

 beaches of Lake Michigan, — observations of a much 

 more precise character than any which, in so far as I 

 know, have been made of such deposits in Europe, — 

 enable him to calculate the time which has elapsed 

 since North America rose out of the waters of the 

 Glacial period as between 5500 and 7500 years. 

 This fixes at least the possible duration of the human 

 period in North America, though I believe there are 



 *' Journal of Geological Society," vol. xxv. 



t *' Silliman's Journal," 1868. i ^ . 



