PALEOGEOGRAPHIC MAPS OF NORTH AMERICA? 
BAILEY WILLIS 
U.S. Geological Survey 
7. PENNSYLVANIAN NORTH AMERICA 
The passage from Mississippian to Pennsylvanian was charac- 
terized by that emergence of lands, which is indicated on the map by 
the districts assigned to continental deposits and temporary lands. 
In the eastern United States the tendency toward emergence was 
progressive though interrupted. In the central west the emergence 
was but temporary and the transient land area was submerged under 
the Pennsylvanian sea. In contrast with the Mississippian, the Penn- 
sylvanian continent probably extended far to the west—north of the 
fortieth parallel. As is shown by White there was land connection 
with England and Europe, probably around the North Atlantic. 
The southeastern portion of the continent appears to have been 
embraced by branches of the equatorial Atlantic current. The 
northwestern part was washed by currents from the Arctic and north 
Pacific. ‘The period was one during which climatic differences devel- 
oped, and the situation of North America favored that development. 
The accumulation of coal in the southeastern portion in contrast 
to red sediments in the southwestern part may thus be explained as 
an effect of climate, in the one district favorable, in the other unfavor- 
able to vegetation. Red beds are to some extent interbedded with 
coal measures, as glacial deposits of the Pleistocene are with inter- 
glacial, and it is probable that the relations may be interpreted as 
evidence of climatic fluctuations.’ 
1 Published by permission of the Director of the U. S. Geological Survey. 
2 Acknowledgments.—The maps of Mississippian and Pennsylvanian North 
America were prepared in conference with Dr. G. H. Girty. As should have been 
stated in the appropriate connection, the maps of Devonian and Silurian geographies 
have been improved by data furnished by Dr. E. M. Kindle. The three earlier maps, 
particularly those of Cambrian conditions, are based on the work of Dr. C. D. Walcott, 
and have been adjusted to the results of his investigations. I am indebted to each of 
these scientists and also to many other fellow-geologists, members of the U. S. Survey 
and others, for suggestions courteously made. They are not responsible, however, for 
the drafts of the maps.—BAILEY WILLIS. 
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