On American Geological History. 419 



m the Jurassic Period along the whole eastern border from Nova 

 Scotia to the Carolinas. Less effect appears in the Cretaceous 

 Period ; and gradually they almost die out as the Tertiary closes, 

 leaving the Mississippi Valley and the eastern shores near their 

 present level. 



Thus were the great features of Middle and Eastern North 

 America evolved ; nearly all its grand physical events, includ- 

 ing its devastations and the alternations in its rochs, were con- 

 sequent upon this system of development. Moreover, as I have 

 observed, this system was some way connected with the relative 

 position of the continent and the oceanic basin. 



We need yet more definite knowledge of the Pacific border 

 of North America to complete this subject. It is in accordance 

 with the fact that the hiirhest mountains are there, that volca- 

 noes have been there in action ; and also that, in the Tertiary 

 Period, elevations of one to two thousand feet took place; and 

 that immediately before the Tertiary, a still greater elevation of 

 the Rocky Mountains across from east to west occurred. The 

 system of changes between the Rocky Mountains and the Pacific 

 has been on a grander scale than on the Atlantic border, and 

 also from a different direction, — and this last is an element for 

 whose influence on the general features we cannot yet make full 

 allowance. 



Through all this time, central British America appears to have 

 taken little part in the operations ; and what changes there were, 

 except it may be, in the Arctic regions, conformed to the system 

 prevailing farther south, for the rocks of the Jurassic Age, like 

 the Connecticut River sandstone, are found as far north as Prince 

 Edward's Island, in the Gulf of St. Lawrence. 



But the Tertiary Period does not close the history of the con- 

 tinent. There is another long Period the Post- tertiary, — the 

 period of the Drift, of the Mastodon and Elephant, of the lake 

 and river terraces, of the marine beds on Lake Champlain and 

 the St. Lawrence, — all anterior to the Human Era. 



From this time there is a fundamental change in the course of 

 •operations. The oscillations are from the north, and no longer 

 from the southeast. 



The drift is the first great event, as it underlies the other loose 

 material of the surface ; and all recognize it as a northern phe- 

 nomenon, connected with northern oscillations. 



