PALEOGEOGRAPHIC MAPS OF NORTH AMERICA" 
BAILEY WILLIS 
U. S. Geological Survey 
II. LOWER CRETACEOUS (COMANCHEAN) NORTH AMERICA? 
In passing from the Jurassic to the Lower Cretaceous North Amer-~ 
ica underwent but little change along the Atlantic border and through- 
out the east. It remained a low land and the coastal plain was some- 
what more deeply submerged. But on the Pacific coast, on the con- 
trary, there was pronounced movement, particularly in the Coast 
Range of California. A bold peninsula developed from Oregon south 
to Santa Barbara and, being eroded, yielded the thick sediments of the 
Shasta group, which were deposited in marine water east of it, in part. 
In Alaska the Shastan sea appears to have invaded the Jurassic 
land widely, but the details are not yet known. 
On the east of the Cordillera, from British Columbia to Wyoming, 
coal-bearing continental deposits (Kootenie) accumulated in a deepen- 
ing trough. In Wyoming, Dakota, and Nebraska a deposit of sand 
(Lakota) was spread upon the plain. South of this occurs the much 
older Morrison formation, which is regarded as probably Jurassic by 
Stanton and which is overlapped by the marine Comanchean strata of 
the gulf. The Kootenie, Lakota, and Morrison are comprised in the 
area mapped as continental deposits.. 
The striking feature of Comanchean geography is the expansion 
of the Gulf of Mexico toward the west and northwest and the deep 
subsidence of its floor, upon which accumulated a remarkable thick- 
ness of limestone. ‘The unusual calcareous deposit of organic remains 
indicates the rich life of an equatorial ocean current. 
The fauna of the Gulf of Mexico in Comanchean time is entirely 
unlike that of the Pacific coast. No adequate explanation of this fact 
has been suggested except that a land mass diverted the ocean current. 
The position of the supposed land was southwest of Mexico and is 
indicated by the dotted area. 
1 Published by permission of the Director of the U. S. Geological ee 
2 Map prepared in collaboration with Dr. T. W. Stanton. 
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