THE SUCCESSION OF DEPOSITS. 35 



Cordilleran Region. Region of the Great Plains. 



probably formed at tliis time, shore-line during this period of 

 though perhaps in part during the rest, 

 second maximum of glaciation. 



Simultaneous elevation of the 

 Renewed elevation of the Cor- g^eat plains to about their pres- 

 dilleran region with one well ^nt level, M'ith final exclusion of 

 marked pause, during which the waters in connection with the sea. 

 littoral stood about 200 feet lower ^^^^ Agassiz formed and even- 

 than at present. Glaciers much ^^^^^^y drained toward the close of 

 reduced and diminishing, in con- t^^s period. This simultaneous 

 sequence of general amelioration movement in elevation of both 

 of climate toward the close of the g^e^t areas may probably be con- 

 glacial period. nected with the more general 



northern elevation of land at the 

 close of the glacial period. 



The tendency of recent observations has been to show 

 that the Pliocene and older subdivisions of the Tertiary 

 covered each of them a much longer time than the 

 Pleistocene, and that the close of the latter approaches 

 more nearly to the modern or recent time than had 

 previously been supposed. To these points we shall have 

 occasion to refer in the sequel. 



It may be proper here to indicate the general nomen- 

 clature which will be followed. When the whole geological 

 series is divided into Primary, Secondary and Tertiary, 

 the deposits to which this paper relates are usually named 

 Post-tertiary or Quaternary. These terms are, in my 

 judgment, unfortunate and misleading. If we take the 

 relations of fossils as our guide, then, as Pictet has well 

 remarked, whether we regard the land or the sea animals, 

 there is no decided break between the newer Pliocene 

 and the Pleistocene, the changes not being greater than 

 those between the Pliocene and the older Tertiary ages. 

 There is, therefore, no such thing in nature as a Quater- 



