PALEOGEOGRAPHIC MAPS OF NORTH AMERICA’ 
BAILEY WILLIS 
U. S. Geological Survey 
8. LATEST PALEOZOIC NORTH AMERICA?’ 
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 
« Published by permission of the Director of the U. S. Geological Survey. 
2 Map prepared in collaboration with Dr. G. H. Girty. 
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