70 GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
the Carboniferous, but are confined to their base; and it appears, from the descriptions, that 
they extend through the valleys or breaks in the ridges into the valley of the Rio Grande. In 
this valley they are well known, and are exposed along the valleys made by the streams. They 
also appear on the western side of the valley, high up on the sides of the Sierra Madre, being 
found near the summit of the Zuñi Pass, (Camino del Obispo,) atan elevation of over 7,500 feet, 
and farther north the strata are continuous from one side of the range to the other along the 
road to Fort Defiance, through Campbell’s Pass. From the western flank of the chain they 
spread out and underlie the broad table-lands and mesas towards the Colorado, forming the 
sides and beds of all the tributaries to the Colorado Chiquito, which is itself, in the formation 
nearly to its mouth in the Great Colorado. The most western exposure along the route appears 
to be at the base of the great voleano—San Francisco mountain—where the red strata are suc- 
ceeded by a thickly-bedded limestone, which is referred, with some doubt, to the lower Carbon- 
iferous. The formation is exposed in nearly every river-bed and caiion from Delaware mountain 
to the foot of the volcano, a distance of about 950 miles, and over one half of the entire route. 
The highest point at which it is known to occur is that already mentioned. With regard to its 
northern extension little is yet known ; but on the south it has been traced along the Red river 
by Captain Marcy, and near the parallel of 32? by Captain Pope, where it extends along the 
Colorado of Texas to its sources in the Llano Estacado. It is also found along the Pecos river 
and Delaware creek. 
Lithological characters.—The eastern portions of the formation along the Canadian and False 
Washita rivers probably present a greater variety in the texture, color, and mineral composition 
of the strata, than any other part. It is this portion of the formation which contains the 
thickest and most interesting beds of gypsum, and the observations on the lithological charac- 
ters along this part of the line are more numerous than upon any other. It appears, from the 
notes and descriptions, that red is not the only color which the strata present. There are 
grey gandstones and limestones, beds of white, grey, and rose-colored gypsum, and different 
shades of blue and red. Thus blue shales, or blue clays, were the portions of the formation first 
seen a short distance beyond Delaware mountain. Grey sandstone is of frequent occurrence, 
alternating with the red; and at Denudation mountain, beds of white siliceous limestone are 
found at the upper part, and are the hardest portions, while below, strata of red sandstone 
predominate, and are separated by beds of red shale, which split up into thin leaves. The 
color of the marls and clays was frequently observed to be like that of the dregs of wine— lie 
de vin;" they were found near Camp No. 21, and between Camps 22 and 23, and again west of 
the Sierra Madre, near Zuñi. At Camp No. 19 the clays were red and blue, and were rather 
hard, and associated with a brecciated sandstone. Fragments of dolomite were also seen. 
Beyond there, white clay was found above gypsum, and a bed of very hard sandstone, coarse- 
grained and feldspathic. The red or wine-colored clays near Camp 22 were overlaid by a sandy, 
red, brecciated limestone, passing into a reddish-grey sandstone. 
. The soft marls were observed, in many instances, to pass into sandstone by becoming more 
sandy, as near Camp 23, where saliferous marls were found to become so sandy that a true red 
sandstone with an alternation of grey was formed. Marls were again observed to pass into 
fine red sandstone and into red siliceous limestone between Camps 24 and 25. Near Camp 29 
the strata of red sandstone were nearly 150 feet thick, and at Camp 30 the following section 
was obtained in the bank : 
Argillaceous dolomite 6 feet 
White gypsum 25 ‘+ 
Sandstone and argillaceous shales and red clay......... Bm 
The red sandstone and red clay appear to predominate at all the localities of gypsum, but 
near Camp 42, green and red saliferous marls occur, and cliffs of white sandstone, a little rose- 
colored, are found along the creeks. Along Rio Bonito this sandstone was found to contain 
calcareous concretions and beds of white limestone. At Arroyo Amarillo, (Yellow creek,) some 
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