THE TRIASSIC PERIOD 



209 



Western Interior. — The large area of sedimentation in this 

 part of the continent had little or no connection with marine 

 waters. Conditions of deposition of later Permian time appear to 

 have been continued through Triassic time, that is, continental 

 deposits were formed mostly in salt lakes, fresh lakes, and along 

 stream courses, while some may even have been wind-blown. 



Pacific Coast. — Since fossils show the strata of the Pacific 

 Coast to be chiefly of marine origin, it is evident that sea water 



Fig. 124 

 The steep western front of the Holyoke Range as seen from 

 Easthampton, Massachusetts. The upper portion is 

 columnar lava of Triassic age, and this rests upon Tri- 

 assic red sandstone. (W. J. Miller, photo.) 



spread over the areas where these strata now occur (see map Fig. 

 123). Igneous rocks in the Triassic of British Columbia prove that 

 there was considerable vulcanism there during the period. 



Close of the Triassic. — The Triassic closed in eastern North 

 America with crustal disturbances which raised the basins of depo- 

 sition of the Newark series into dry land, thus leaving all of the 

 eastern half or two-thirds of the continent dry land and undergoing 

 erosion for the first time since the beginning of the Paleozoic era. 



On the Pacific Coast the evidence is pretty clear that marine 

 conditions continued as during the period, while in the western 

 interior the geographic conditions toward the close of the Triassic 



