Paleogeographic Maps of North AmericaAuthor(s): Bailey WillisSource: The Journal of Geology, Vol. 17, No. 5 (Jul. - Aug., 1909), pp. 403-405Published by: The University of Chicago PressStable URL: http://www.jstor.org/stable/30055780 .

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PALEOGEOGRAPHIC MAPS OF NORTH AMERICA'

BAILEY WILLIS U. S. Geological Survey

8. LATEST PALEOZOIC NORTH AMERICA2

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.

403

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404 BAILEY WILLIS

NORTH AMERICA\\

SLEGEND

OCEANIC BASINS

LATEST PALEOZOIC

MARINE WATERS (EPICONTINENTAI)

SEA OR LAND MORE LIKELY SEA LAND OR SEA MORE LIKEL LA;D'

t LANDS

INDETERMINATE AREAS

MARINE CURRENTS POLAR EQUATORIAL

CONTINENTAL DEPOSITS, SOMETIMES INCLUDING MARINE SEDIMENTS

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PALEOGEOGRAPHIC MAPS OF NORTH AMERICA 405

south warm. The vertebrates known from Nova Scotia to Texas appear to have lived in the more genial regions and to have had no communication (unless closely following the Pennsylvanian) with Europe or South America, although the latter was connected with Africa by some southern route. The barriers to intermigration in the north may have been marine waters (North Atlantic) and cold climate (Alaska-Siberia).'

' My thanks are due to Dr. S. W. Williston for discussion of the evidence regarding vertebrates.-B. W.

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