PALEOGEOGRAPHIC: MAPS OF (NORTH AMERICA: 
BAILEY WILLIS 
U. S. Geological Survey 
I2. UPPER CRETACEOUS NORTH AMERICA? 
North America was submerged over extensive areas during the 
Upper Cretaceous. From Cape Cod to Texas the Atlantic and Gulf 
coasts of the preceding period were transgressed by the sea. From 
the Gulf to the Arctic marine waters spread over what is now the site 
of the Great Plains and in the United States that of the Rocky Moun- 
tains. ‘The Pacific extended its limits in California and Oregon; 
farther north, however, from British Columbia to Alaska the land 
gained. 
In the central West, from New Mexico to Alberta the invasion of 
the sea was followed by emergence of the area ruled on the map for 
continental deposits. The surface of the area was built up by sedi- 
ments which were derived from uplands west of it, and which accu- 
mulated about as fast as the bottom sank. ‘The area thus formed a 
coastal plain, extensive marshes prevailed, and the marsh deposits 
eventually became coal beds. Sea, marshes, and river plains alter- 
nated in sequence till near the close of the Cretaceous period, when 
in this Rocky Mountain area certain spots became mountains, the 
forerunners of the Colorado Front Range, the Black Hills, and Big- 
horn Mountains of today. 
East of the Rocky Mountain coastal plain the marine strait pre- 
vailed to the end of the period. It divided the continent, reduced the 
northern land area, and admitted warm waters to the Arctic. These 
conditions favored the mild climate which the northern regions then 
enjoyed. 
The eastern portion of the continent contrasted with the western. 
Whereas in the west rising lands were eroded, carved into hilly or 
1 Published by permission of the Director of the U. S. Geological Survey. 
2 Map prepared in collaboration with Dr. T. W. Stanton. 
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