LIMESTONES WEST OF SAN FRANCISCO MOUNTAINS, 69 
storms, and the ground was so generally covered, that the accurate determination of the geo- 
logical structure was difficult if not impossible. 
r. Marcou speaks of finding, under the lava in the immediate vicinity of Partridge and 
Cedar creeks, the ‘‘magnesian limestone’ (Permian) and ‘‘carboniferous sandstones’? —the equiv- 
alents of the coal measures; and beneath them the ‘‘mountain limestone,’’ with Productus semi- 
reticulatus, Terebratula sublilit, &c. &c. A few miles further west, after passing over surfaces 
occupied by carboniferous sandstones, and seeing the mountain limestone exposed in many 
localities, he reached an escarpment composed of granite from base to middle, then red sand- 
stones, which he calls Devonian, ‘‘above which are beds of limestone and gray sandstone 
belonging to the mountain limestone.’’ No fossils were found in the sandstones. 
Unfortunately, Mr. Marcou’s notice of this interesting section is very brief. This is deeply 
to be regretted, as the important truths there taught in reference to the original extent and 
mode of formation of the table-lands are left to the contingency of a visit to that far-off and 
inhospitable region by some competent geologist, who will make full and accurate observations, 
and for his conclusions give us satisfactory proofs. 
There would be no objection to the acceptance of Mr. Marcou’s unqualified assertion that 
here were exposed the Devonian sandstones and the Mountain or Lower Carboniferous limestone, 
were it not that the evidences of geological age which induced his decision are of at least ques- 
tionable value; and there are strong reasons, judging from the exposures examined by us, 
especially that in the cafion of the Colorado, for suspecting that the strata composing the 
section described by Mr. Marcou are not older than the Carboniferous epoch. By reference to 
the sections of the cafion of the Colorado, that of the high mesa at Camp 70, and of the cajion 
of Cascade river, all of which are given in detail in the preceding chapter, it will be seen that 
the oldest palzozoic strata, those resting on the granite in the bottom of the basin of the 
Little Colorado, consist of a series of red sandstones and shales more than a thousand feet in 
thickness, and that these are deposited around—their strata abutting against—the ridges and 
pinnacles of the granite. Above these red sandstones, &c., follow another thousand feet of 
silicious and argillaceous shales, interstratified with thin bands of limestone, clouded red and 
blue, or yellow. Upon this series we, for the first time, met with a massive, thick-bedded, 
gray limestone, a very important constituent of the geological column, having a thickness of over 
a thousand feet. This I have regarded as probably the equivalent of the Mountain limestone. 
On this limestone rests a series of dark red sandstones and red shales, several hundred feet in 
thickness; above them, two hundred feet of gray or drab sandstones; then the crinoidal lime- 
stone, the surface rock over all the western part of the high mesa. 
This latter rock, which is certainly the one exposed on the banks of Partridge and Cedar 
creeks, is frequently referred to in the journal of Mr. Marcon, and is considered by him the 
‘*Lower Carboniferous or Mountain Limestone.’’ Its fossils, however, as will be seen by refer. 
ence to the chapter on Paleontology, prove it to be the equivalent of the Coal measures of the 
Mississippi valley, and more recent than the Mountain limestone. 
Mr. Marcou’s observations were exact, and if the limestone crowning the cliff, noticed and 
figured in his journal of January 22, (Pacific Railroad Report, vol. Ill, Geological Report, p. 156; 
Geology of North America, p. 24,) is, as he says, identical with that of Partridge creek, it is 
evident that all the stratified portion of the section in the cliff referred to is composed of 
Carboniferous rocks, the Middle Carboniferous limestone forming the summit; beneath which, 
precisely as at Camp 70, &c., are the drab and red sandstones. There is scarcely a doubt that 
this is the true reading of the facts. The observations made by our party on three sides of 
the locality in question can scarcely be reconciled with any other conclusion. 
Aside from the complete correspondence between the stratified portions of the section given 
by Mr. Marcou and those of the Middle Carboniferous strata in neighboring localities, there is 
