STRUCTURE OF VALLEY OF LITTLE COLORADO. 75 
among themselves, have certain common characters that serve to form a distinct geological 
horizon, and one readily recognizable wherever it appears. The group consists of sandstones, 
shales, and conglomerates, of which the prevailing color is a deep red, deeper than that of the 
red rocks above or beneath them. To this general rule there are, however, many local excep- 
tions, some members of the series frequently exhibiting a decided green tinge, as in the Navajo 
country, Fort Defiance, Apache cafion east of Santa Fé, &c. This formation is also charac- 
terized by salt springs which flow from it in several localities. Though I examined its members 
in various exposures, I was never able to detect in them a fossil of any kind. In some places 
the compact red sandstones of this series show a striking lithological resemblance to those of 
the valley of the Connecticut and New Jersey, so much used for architectural purposes, while 
the greenish shelly sandstones are scarcely distinguishable from those forming the fish beds at 
Hadley Falls, Mass., Durham, Conn., &c. 
By Mr. Marcou this group is considered the equivalent of the red sandstones of Lake Supe- 
rior and of that portion of the Trias of Europe called by the Germans Bunter Sandstein, by the 
French Grés Bigarré.—( Geology of North America, pp. 10, 11.) 
No American geologist will need to be informed that the sandstones of Lake Superior are of 
the age of the Potsdam of New York, and lie at the base of the Silurian series. It is true 
that there is considerable lithological resemblance between the Potsdam sandstones of Lake 
Superior and those overlying the Carboniferous series in New Mexico; but that fact serves 
simply to show how fallacious are the inferences derived alone from lithological characters. 
There is no evidence opposed to the theory that this group is the equivalent of a portion of 
the Trias of Europe, but it must also be said we have, as yet, little or no evidence in favor of 
it. As a conjecture, this classification is perhaps creditable to its author, but all the data for 
the determination of its truth are yet to be discovered. 
Judging from all the facts now in our possession in reference to this group, it seems quite as 
likely to prove Permian as Triassic. It is, perhaps, still more likely to be both, like the ‘‘ New 
red sandstone formation”’ of the Atlantic States, a series of strata succeeding the Carboniferous 
rocks, plainly the representatives of the Permian and Triassic formations of the Old World, but 
showing nothing of the hiatus which separates them in Europe, and being scarcely susceptible 
of subdivision into exact equivalents of either. 
From my journal I extract the following additional observations on these strata, made in the 
vicinity of the crossing of the Little Colorado: 
‘*‘ May 1.—The limestone over which we have passed, descending from the San Francisco 
mountain, as we approached our present camp, showed a dip to the northeast of at least a 
hundred feet to the mile ; and before reaching the river it passed under beds of red shale and 
sandstone, which are conformable with it. This sandstone is deep blood-red in color, is soft, 
and eroded into fantastic blocks and masses, of which the surfaces are most curiously etched 
and carved by weathering. Above these heavier beds are soft, red, argillaceous shales, with 
layers of red and green, foliated, ripple-marked, fine grained, micaceous sandstones, all without 
fossils. Such is the geology of the south bank of the river. On the north bank the red shales 
appear at intervals, but are usually concealed by alluvial soil, sand, and gravel. About seven 
miles from the river the valley is bounded by a mesa wall nearly one thousand feet in height, 
of which the base is formed by the red shales and sandstones before described.”’ | 
A portion of this series, which is concealed by the alluvium near Camp 85, is more fully 
exposed further up the river. Near Camp 88 a butte, representing a portion of the upper part, 
consists of, first, conglomerate, a coarse light-brown sandstone, with white, bluish, red, and 
black quartz pebbles, varying in size from that of a pea to an egg. It is about twenty feet = 
thickness, and lithologically. both as regards the paste and the pebbles, quite undistinguishable 
from much of the Carboniferous conglomerate in Ohio and Pennsylvania. Below this rock is a 
reddish white, rather shelly, micaceous sandstone, of which over thirty feet are exposed. 
