PALEOGEOGRAPHIC MAPS 



BAILEY WILLIS 

 U. S. Geological Survey 



8, 9, AND 10. LATEST PALEOZOIC/ TRIASSIC, AND LATE JURASSIC^ 



North America during the latest Paleozoic, the period which 

 corresponded in a general way with the Permian in Europe, was an 

 expanding land. On the east the Appalachian peninsula had been 

 eroded during Pennsylvanian time and erosion continued vigorously 

 during the later Paleozoic. The elevation which gave the process of 

 erosion this opportunity was probably due to pressure from the Atlan- 

 tic, that raised all the eastern margin and exposed any then existing 

 coastal plain, out to the edge of the continental shelf. The pressure 

 ultimately occasioned the displacements apparent in the folded and 

 overthrust zone of the Appalachian and St. Lawrence valleys, and it 

 is probable that the continental margin on the Atlantic side was then 

 moved westward to near its present position, the oceanic basin expand- 

 ing westward to an equal amount. 



In the eastern central United States the area of continental deposits 

 shrank within narrower limits. The condition of the Mississippi 

 embayment is unknown. 



In the northwest the land extended, apparently, nearly if not quite 

 to the Pacific; but in southern Alaska the sea prevailed. 



The island which stretched from Colorado to southern Arizona 

 obstructed to some degree the general distribution of the red sedi- 

 ments, chiefly of continental character, which were derived from the 

 wide lands to the northwest, north, and northeast. The island also 

 separated the northern embayment of waters which were probably 

 cool from the southern sea, through which flowed a warm current; 

 and thus it divided two faunal districts. 



The geographic conditions and the independent evidence of cli- 

 matic diversity indicate that the north was cool, if not cold, and the 



1 Map prepared in collaboration with Dr. G. H. Girty. 



2 Map prepared by Dr. T. W. Stanton; modified, as regards marine connection 

 between the Pacific and the Arctic in the Mackenzie Valley, by Bailey Willis. 



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