396 Colorado River of the West. 
The numerous great gorges and profound cafions cut by the ero- 
sive action of water, through thousands of feet of strata, in a — 
district where the rocks have, for the most part, suffered little or 
no disturbance since their deposition, afforded him a fine oppor- 
tunity to study its geological structure. Probably in no other 
rt of the world can so great a thickness of strata be seen and 
examined inch by inch in one continued section as here. 
tremendous chasms cleaving the beds, as they do almost vernoae . 
sometimes to the astonishing depth of from three to six thousan 
feet, reveal every bed and layer of rock from top to base, 
clearly and distinctly as they can be seen in the artificial excava- 
tions along our rail-roads. 
In the great Caiion of the Colorado, on a high mesa, west of 
the Little Colorado, Dr. N. saw at a single exposure in re 
succession the following formations: 
1st. Upper Carboniferous limestoae surmounting beds of cross- 
stratified sandstones, and red calcareous sandstones with gypsum, . 
altogether, 1200 feet. pt 
2d. Lower Carboniferous limestone, 1000 feet. A 
3d. A great thickness of limestone shales, and grits, apparently 
of Devonian age, resting upon heavy deposits of limestone, mu 
rocks, and sandstones, apparently of Silurian age, with a sand- 
stone at the base, probably representing the Potsdam sa 
of New York: the whole not less than 2,300 feet. 
Beneath all these stratified rocks the gorge is excavated 80 8 
to expose 1000 feet of granite. oF 
Of these rocks Dr. Newberry remarks that, “ the Silurian an 
Devonian strata are entirely conformable among themselves, a0 
with the Carboniferous rocks. They lie nearly horizontal upon 
the granite, forming a series of sandstones, limestones, and shales, 
about 2000 feet in thickness. The Carboniferous series el 
sists of over 2000 feet of limestones and gypsum, apparently y 
massive, and often highly fossiliferous. The upper mem! tle 
of the latter series form the surface of the mesas of the Lit 
rada, upon which the volcanic group of the San Francisco 
mountains rest as a base.” + athe 
At other localities Dr. N. had opportunities to axe sad, 
succeeding formations above those jnst alluded to. One of ‘ ny 
at the crossing of the Little Colorado, where one side of ae? ts 
ley is formed by a third mesa wall, which with the slope ight 
ase rises to an elevation of at least one thousand feet in he 
above the stream. 
et YS id i _ shales, and 
_*This mesa,” he says, “is composed of deep-red sandstones, 
conglomerates, resting conformably on the Upper Carbonifero , 
over which is a series of variegated marls, with bands of magnesi 
stone. The latter series forms the surface of the mesa for many 
miles 
and has an aggregate thickness of perhaps 1,600 
