THE TRIASSIC PERIOD 687 



Close of the Trias 



Considerable geographic changes marked the close of the Trias- 

 sic period in eastern North America, bringing the areas which had 

 been the sites of deposition to higher levels, faulting the rocks, 

 and affecting them by igneous intrusions. These changes were 

 comparable in extent and importance to the changes which separate 

 the various systems of the Paleozoic, but they were not of conti- 

 nental extent. 



In the western part of the United States, the separation of the 

 Triassic period from the Jurassic was not pronounced, and the sedi- 

 mentary history of much of the western half of the continent seems 

 to have run an uninterrupted course from the beginning of the 

 Permian to the later part of the Jurassic. The case may have 

 been somewhat different north of the United States, for in British 

 Columbia and in the adjacent islands, Triassic and older formations 

 were upturned, deeply eroded, and again submerged before the 

 beginning of the Cretaceous. The great igneous formations asso- 

 ciated with the Trias of the northwest appear to have been made 

 during the Triassic period, rather than at its close. 



FOREIGN TRIASSIC 

 Europe 



In Europe, the Trias is exposed in many widely separated 

 places, the largest being in northwestern Russia; but the system 

 is better known in the western part of the continent. In England, 

 it is unconformable on the Permian, but on the continent, generally 

 conformable. 



The system has a marine and a non-marine phase. The non- 

 marine (or Triassic) phase prevails throughout the northern part 

 of the continent, while the marine (or Alpine) phase is found 

 farther south. The former resembles the Permian of Europe, and 

 the Permian and Triassic of the United States. 



In general, the Upper Trias is more wide-spread than the Lower, 

 especially in the southern part of the continent, and is marine over 



