ORIGIN OF SEDIMENTARY STRATA. 47 
the present streams are but miniature representatives of those which formerly flowed in their 
channels. 
Everything indicates that the table-lands were formerly much better watered than they now 
are. 
AREA AND LIMITS OF THE PALZOZOIC CONTINENT. 
The question of the origin of the sediments composing the stratified rocks of the table-lands 
of the Colorado can scarcely be intelligently discussed till we know more than we now do of 
the geology of a large area lying north of the Colorado, and of the broad and compound belt of 
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. 
is much, however, we can fairly infer from the observations already made on the geological 
structure of the far 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 continen- 
tal surfaces of dry land. 
Since the erosion of rocks is always subaerial, or at least never takes place more than forty 
feet below the ocean surface, it follows that to form the stratified rocks of only that portion of 
the great central plateau which borders the Colorado, an island 300 miles in diameter, and at 
least 6,000 feet high, or, what is more probable, a continent of six times that area and 1,000 
feet high, was worn down by the action of waves and rains, and in the form of sediments, sand, 
gravel, clay or lime, deposited on the sea bottom. 
When we reflect that, with the exception of narrow wedges of erupted material in the 
mountains, an area having, on the 36th parallel, the breadth of the entire distance between the 
great bend of the Colorado and the Mississippi, (1,200 miles, ) and a great, though yet unmeasured 
extension north and south is occupied by several thousand feet of Paleozoic and Secondary 
strata, we must conclude that these sediments have not been derived from the erosion of 
emerged surfaces east of the Mississippi, but here formed by the incessant action of the Pacifi 
Waves on shores that perhaps for hundreds of miles succumbed to their power and by broad 
and rapid rivers which flowed from the mountains and through the fertile valleys of a primeval 
Atlantis, 
I have already alluded to the absence of the Silurian and Devonian rocks from the sections 
on the flanks of the Rocky mountain axes in New Mexico, while they occur in great thick- 
ness in the sections of the ca on of the Colorado, and that they were deposited around, and 
abutting in horizontal stratification against, the granitic spurs of the mountains bounding the 
table-lands on the west; and further, that the axes of these mountains are on the east side 
flanked by Carboniferous strata resting on the granite; the Silurian and Devonian rocks being 
absent. These facts show that the older Paleozoic strata were deposited in a trough or basin 
bounded on the east and west by granitic mountains which rose above the ocean’s surface. 
The Potsdam (?) sand stone which is largely developed in the Great Cafion is a coarse silicious 
rock that must have been derived from the erosion of land at no great distance. 
It is true that the Silurian, Devonian, and Lower Carboniferous limestones are, where I 
examined them, nearly destitute of fossils, and seem to be deep-sea deposits, but shore lines 
would doubtless, by proper search, be found, where fossils are abundant, within.a few miles of 
the localities where these strata are exposed on our route. 
It would seem that in that vicinity (mouth of Diamond river) the water shoaled by the 
deposition of the sediments forming the older rocks, as the overlying Carboniferous strata 
abound in fossils, and one of the members of that series, a sandstone, everywhere affords striking 
evidence of current action in its cross stratification. 
