PALEOGEOGRAPHIC MAPS OF NORTH AMERICA? 
BAILEY WILLIS 
U. S. Geological Survey 
Q. TRIASSIC NORTH AMERICA 
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. 
1 Published by permission of the Director of the U. S. Geological Survey. 
406 
Ms ser ry 
