Paleogeographic Maps of North AmericaAuthor(s): Bailey WillisSource: The Journal of Geology, Vol. 17, No. 5 (Jul. - Aug., 1909), pp. 406-407Published by: The University of Chicago PressStable URL: http://www.jstor.org/stable/30055781 .

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PALEOGEOGRAPHIC MAPS OF NORTH AMERICA'

BAILEY WILLIS U. S. Geological Survey

9. TRIASSIC NORTH AMERICA

In Triassic time North America attained a larger connected land area than at any known epoch of its earlier history. The eastern region was apparently subject to erosion till the close of the period, when the continental or estuarine deposits of the Newark group gath- ered in basins near the probable margin.

Lower Triassic marine strata occur in southwestern Idaho in an area mapped as occupied chiefly by continental deposits. The prin- cipal epicontinental seas, however, appear to have formed embayments in British Columbia and west of longitude 1150 in the United States. They were probably not connected. Southern Alaska was submerged and Behring Strait also.

With the close of the Triassic the embayments upon the continen- tal plateau appear to have become land and the continent attained in the early Jurassic a still greater expansion. Both eastward and west- ward it exceeded its present coasts in middle latitudes and no part of the intervening continent was submerged.

The Triassic continental deposits indicate an arid climate in the central west; whereas on the southeastern Atlantic border there was a humid climate in which marsh conditions prevailed.

' Published by permission of the Director of the U. S. Geological Survey.

406

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PALEOGEOGRAPHIC MAPS OF NORTH AMERICA 407

'TRIASSIC NORTH AMERICA

LEGEND OCEANIC BASINS

MARINE WATERS (EPICONTINENTAI,)

SEA OR LAND. MORE LIKELY SEA LAND OR SEA. MORE LIKELY LAND

SLANDS

INDETERMINATE AREAS

MARINE CURRENTS POLAR EQUATORIAL

CONTINENTAL DEPOSITS, SOMETIMES INCLUDING MARINE SEDIMENTS

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