CARBONIFEROUS LIMESTONE, 73 
The chemical composition of this rock is no proof of its identity with the Magnesian limestone 
of Europe, as most of the limestones of the far west are more or less dolomitic; and so are many 
of the limestones of the Coal measures in the valley of the Mississippi. Even if it should be 
proved that the red sandstones and shales overlying it are Triassic, of which, as yet, we have 
no satisfactory evidence, it by no means follows that it is of Permian age. In many localities 
in New Mexico, examined by Mr. Marcou or myself, east of this point, the red sandstones and 
variegated marls (Trias of Marcou) rest directly upon the Carboniferous limestones. Every 
geologist knows that the geological column is nowhere complete, but that, in every known 
locality, either entire formations or important sub-divisions are wanting, though the superior 
and inferior strata may be fully represented. 
Coming, asI did, to the examination of the rock in question from the clear and beautiful 
exposures of the Carboniferous strata described in the preceding pages, I detected in it no new 
element, and did not hesitate to consider it a portion of that series. It is possible that when 
the vicinity comes to be more fully explored there may be found in this rock fossils of Permian 
character, as in Kansas the Upper Carboniferous strata contain a few prophetic types of the 
succeeding Permian fauna; but probably then, as now, it would be impossible to draw any line 
of separation between the strata of limestone immediately underlying the red sandstone, on the 
Little Colorado, and those a few feet below, which are conformable with and lithologically 
undistinguishable from them, and which are purely Carboniferous. At present it is not saying 
too much to assert that we want the first shadow of proof of the Permian age of the rock in 
question, and, with the knowledge we now have, it is plainly required of us to regard it as an 
integral portion of the Carboniferous series. 
10——L 
