No. 136.] 81 



meet the difficulties of the case, and that the facts of the Drift 

 form one of the most obscure and perplexing questions in all 

 geological investigation. 



Above the gravel beds, near the St. Lawrence and Lake Cham- 

 plain, are some beds of clay, two hundred feet thick or more, 

 which contain marine shells of species now existing on the coast 

 of New-England and Canada. These prove that since such shells 

 were living, those valleys must have been depressed below the 

 sea-level, long enough for these deposits of clay to be formed. 

 They are known as the Pleistocene* clays. (The Albany clays 

 are their southern extension, but contain no fossils.) Specimens 

 of the shells of this Pleistocene are in case. 



* Pleistocene, from two Greek words signifying *^the most recent," because they are 

 the newest of all marine deposits known in the State. 



[Assembly, No. 136.] 11 



