348 The American Geologist. December, 1893 
were of marine origin until towards the close of the period when a 
prolonged orographic movement elevated a large area of the continent 
above sea level and locally upturned the Cretaceous strata in the 
Rocky mountain area. The shoaling of the sea was followed by the 
formation of great inland lakes in which fresh water deposits succeed- 
ed the marine and estuarian sediments. Over the coastal regions they 
were of marine origin throughout. 
The Tertiary sediments deposited on the Cretaceous are marine on the 
Atlantic, Gulf of Mexico and Pacific coasts, and of fresh water origin 
in the Rocky mountain and Great Plains areas — where they were depos- 
ited in the great inland lakes outlined in the previous period. 
Geogbaphio Conditions accompanying the Deposition of Paleozoic 
Sediments in the Cordillekan Sea. 
The assumed area of the Cordilleran or Paleo Rocky Mountain sea 
includes over 400,000 square miles between the 35th and 55th parallels. 
To the eastward, during lower and middle Cambrian time a land 
area is thought to have extended from east of the 111th meridian across 
the continent to the Paleo-Appalachian sea. This land was depressed 
toward the close of middle Cambrian time, and theMississippiansea ex- 
panded over the wide plateau-like interior region, from the gulf of 
Mexico on the south to the lake Superior region on the north; westward 
it penetrated among the mountain ridges between the 105th and 111th 
meridians, laying down the upper Cambrian deposits that are now found 
in New Mexico, Arizona, eastern Utah, the western half of Colorado, 
Wyoming, Idaho, and Montana, and still further northinto Alberta and 
British Columbia. During Ordovician, Silurian, Devonian and 
Carboniferous time this entire Mississipian region, except portions in 
Devonian time, appears to have been covered by a relatively shallow 
sea that was coextensive with the Appalachian sea and that communi- 
cated freely with the Cordilleran sea. During this same age, however, 
the Rocky mountain area of New Mexico, Colorado, Utah, Wyoming 
and Montana formed a more or less well defined boundary of ridges and 
islands between the Cordilleran and the interior sea up to the 49th par- 
allel. To the north of the latter the conditions appear to have been 
the same as on the eastern side of the continent, where the Appalachian 
sea communicated freely with the Mississipian sea. From the data that 
we now have I think that the Paleozoic (Mississipian) sea extended at 
times over nearly all of the area subsequently covered by the Cretaceous 
and the later formations between the gulf of Mexico and the Arctic 
ocean. This belt is bounded almost continuously on the east and west 
by Paleozoic rocks that extend from the Arctic ocean to Mexico, and 
whether of Cambrian. Ordovician, Silurian or Devonian age they carry 
essentially the same fauna throughout their extent. In the outcrops of, 
lower strata that rise up through this Cretaceous area, the Cambrian, 
Ordovician and Carboniferous rocks are found encircling thepre-Paleo- 
zoic rocks. Instances in which the Archean rocks have been met with 
immediately beneath the Cretaceous in borings in Dakota and Minne- 
