178 BAILEY WILLIS 



south warm. The vertebrates known from Nova Scotia to Texas 

 appear to have lived in the more genial regions and to have had no 

 communication (unless closely following the Pennsylvanian) with 

 Europe or South America, although the latter was connected with 

 Africa by some southern route. The barriers to intermigration in 

 the north may have been marine waters (North Atlantic) and cold 

 climate (Alaska-Siberia).' 



In Triassic time North America attained a larger connected land 

 area than at any known epoch of its earlier history. The eastern 

 region was apparently subject to erosion till the close of the period, 

 when the continental or estuarine deposits of the Newark group gath- 

 ered in basins near the probable margin. 



Lower Triassic marine strata occur in southwestern Idaho in an 

 area mapped as occupied chiefly by continental deposits. The prin- 

 cipal epicontinental seas, however, appear to have formed embayments 

 in British Columbia and west of longitude 115° in the United States. 

 They were probably not connected. Southern Alaska was submerged 

 and Behring Strait also. 



With the close of the Triassic the embayments upon the continen- 

 tal plateau appear to have become land and the continent attained in 

 the early Jurassic a still greater expansion. Both eastward and west- 

 ward it exceeded its present coasts in middle latitudes and no part of 

 the intervening continent was submerged. 



The Triassic continental deposits indicate an arid climate in 

 the central west; whereas on the southeastern Atlantic border there 

 was a humid climate in which marsh conditions prevailed. 



The very extensive land area which North America presented 

 during a part of the Jurassic period was reduced in the late Jurassic 

 by marine invasion from the Pacific. The sea transgressed to western 

 Nevada. It apparently occupied much of British Columbia, but the 

 subsequent intrusion of the great batholith of the Coast Range 

 destroyed the record near the coast. Further inland volcanic effusive 

 rocks are associated with marine sediments, which on meager paleon- 

 tological evidence are classed by Stanton as probably Jurassic and by 

 Whiteaves as "Lower" Cretaceous. 



I My thanks are due to Dr. S. W. Williston for discussion of the evidence regarding 

 vertebrates. — B. W. 



