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Colorado River of the West. 399 
mountains, which we have covered by a single name, (Rocky mountains,) 
but which, when carefully studied, will probably not be found to form a 
geological unity. 
This much, however, we can fairly infer from observations already made 
on the geological structure of the tar west, viz: That the outlines of the 
western part of the North American continent were approximately marked 
out from the earliest Paleozoic times; not simply by areas of shallower 
water in an almost boundless ocean, but by groups of islands and broad 
cafion of the Colorado, and that they were deposi 
in horizontal stratification agains 
i ble-] 
on the granite; the Silurian and Devonian rocks 
facts show that the older Paleozoic strata were 
basin ed on the east and west 
ove the ocean’s surface. ; ‘ 
The Potsdam (!) sandstone which is largely —— ee gen 
Cafion is a coarse silicious rock that must have been deriv m the 
erosion of land at no t distance. 
It is true that sha Siluviats Devonian, and Lower Pa ea — 
mined them, nearly destitute of fossils, and seem 
deep-se i shore lines would doubtless, by proper search, 
found, where fossils are abundant, within a few miles of the localities 
where these strata are xposed on our route. : 
It would sein thal in that vicinity (mouth of Leoagreapr gd the ag 
shoaled by the deposition of the sediments forming the older rocks, as as 
overlying Carboniferous strata abound in fossils, and one of the mem 
