PALEOGEOGRAPHIC MAPS OF NORTH AMERICA? 
BAILEY WILLIS 
U. S. Geological Survey 
5. MIDDLE DEVONIAN NORTH AMERICA 
The archipelagic condition of North America which began in 
the Ordovician persisted through the two succeeding periods with 
many changes of land and sea. Any refined study of these changes 
involves somewhat precise correlations which have already been 
carried far. The map here presented is of one passing phase only. 
The time represented is that before and after the invasion of the 
Hamilton fauna into the New York embayment, as is indicated by 
the temporary land barrier shown in Illinois and Missouri. The great 
thickness of sediments in the eastern Appalachian trough indicates 
marked orogenic movement during the middle and upper Devonian 
in the land lying toward the Atlantic. The southeastern expansion 
of the sea over Appalachia began apparently in middle Devonian 
and extended into upper Devonian time. 
6. MISSISSIPPIAN NORTH AMERICA 
The distribution and character of the Mississippian sediments 
leads to the inference that the time was one of an extended epicon- 
tinental sea with low and relatively hmited lands. The archipelago 
of the immediately preceding period gave way to a general sub- 
mergence of all the southwestern portion of the continent. In the 
far north conditions were favorable to the deposition of coal and other 
continental deposits associated with marine beds. The Atlantic _ 
and eastern portion of the interior sea and the wide sea covering all 
the western states present differences of habitat which are empha- 
sized by Dr. Weller in his discussion. ‘Toward the close of the 
Mississippian or early in Pennsylvanian time, an extensive land 
area emerged in the Colorado-New Mexico region, as indicated by 
erosion of the Mississippian sediments. 
« Published by permission of the Director of the U. S. Geological Survey. 
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