PALEOGEOGRAPHIC MAPS*OF NORTH AMERICA? 
BAILEY WILLIS 
U.S. Geological Survey 
IO. LATE JURASSIC NORTH AMERICA? 
The very extensive land area which North America presented 
during a part of the Jurassic period was reduced in the late Jurassic 
by marine invasion from the Pacific. ‘The sea transgressed to western 
Nevada. It apparently occupied much of British Columbia, but the 
subsequent intrusion of the great batholith of the Coast Range 
destroyed the record near the coast. Further inland volcanic effusive 
rocks are associated with marine sediments, which on meager paleon- 
tological evidence are classed by Stanton as probably Jurassic and by 
Whiteaves as “Lower” Cretaceous. 
Communication of Pacific waters through the Arctic with the seas 
of eastern Europe and Asia is indicated by similar boreal species in 
both regions, but the connection is not known. It may have been by 
Behring Sea, as Stanton thinks probable, or by the Mackenzie, as 
Willis infers. 
Marine waters (the Sundance sea) extended temporarily to Dakota, 
Wyoming, and southern Utah. 
On the east the continent was low. The lower part of the Potomac 
formation, long considered to be late Jurassic, is according to the 
latest work under W. B. Clark probably “Lower” Cretaceous 
(Comanche). The limit of the coastal plain is therefore unknown. 
It was beyond the present coast. 
t Published by permission of the Director of the U. S. Geological Survey. 
2 Map prepared by Dr. T. W. Stanton; modified, as regards marine connection 
between the Pacific and the Arctic in the Mackenzie Valley, by Bailey Willis. 
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