62 GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
blue, and sometimes black. It is very compact, and breaks with a conchoidal fracture. Some 
of the strata are very thin, and are intercalated with black clay-shales. It is reported that a 
short distance further south it contains beds of bituminous coal. At another point, where the 
mountains were ascended, the limestone was greyish-white, or blackish. At the outcrop on 
the summit of the Sierra Madre, the limestone was found to be bluish-grey ; and further west, 
beyond the Colorado Chiquito, the limestone of Cafion Diablo is of a similar color, or rather 
more white and yellowish, as I am assured by Mr. Campbell. At Camp 97, the rock is said to 
contain siliceous kidney-shaped masses, which have been baked to a rose-color by the hot melted 
lava. The other and most western outcrops in the Aztec range probably have the same 
bluish-grey color, as this is the color of the fossils, and I do not find any observations on the 
color of the beds at that place. The fossils are, however, lighter-colored than those from 
the Pecos villages. 
The strata at nearly all the localities appear to alternate with thin beds of shale or sand- 
stone. At Delaware mount the limestone alternates with sandstone, and at Albuquerque 
mountains with thin and black clay shales, at one place from four to six feet thick. Beds of 
very hard and rose-colored sandstone were also found—one of them being composed of coarse 
rolled grains. The limestone of the Sierra Madre was also found to alternate with beds of 
roseate sandstone. The rock of Cañon Diablo is hard and compact, and is filled with small 
pits, leaving sharp and hard angles. Kidney-shaped masses of black silex were found in the 
limestone beds of the Sandia mountains ; and similar nodules occur in the strata near Camp 96, 
where they have become discolored by the heat of the lava. 
Thickness of the strata.—Mr. Marcou estimates the thickness of the limestone, and included 
beds of sandstone, at Delaware mountain, as from five to six hundred feet, and near Camp A, in 
the cañon of San Antonio, (Sandia mountains,) at three hundred feet; but he again estimates 
-the thickness of the Carboniferous, probably including the sandstones and shales above the lime- 
stone, at two thousand feet. There are no notes upon the thickness of the strata at the summit 
of the Sierra Madre, nor is the thickness of the limestone at the cliff in the Aztec range men- 
tioned, but the combined thickness of the whole formation is represented as about six hundred 
feet. It is undoubtedly the fact that the beds become thinner towards the west. The strata of 
Cañon Diablo, according to Mr. Campbell, are from three feet to eight or ten in thickness, and 
the cañon has a depth of 125 feet, and is wholly in the limestone. y 
Fossils.—The limestone contains a great abundance of fossils at the Pecos villages, and in the 
cañon of San Antonio. They are also numerous west of the volcano of San Francisco, but are 
not so well preserved. At Delaware mountain the rock is charged with the stems of encrinites, 
which are crystalline carbonate of lime, while the surrounding rock is granular. Mr. Marcou 
mentions finding Terebratule and Polypi at this place, and an Orthis is found in the collection— 
No. 124 of the catalogue and description. The greater part of the fossils in the collection are 
from the Pecos villages, Santa Fé mountains. They were all submitted to Professor Hall for 
his examination, and the descriptions of them will be found in ChapterIX. They consist of the 
following species: Productus semireticulatus, P. pustulosus, Terebratula subtilata, T. roissyi, T. 
millipunctata, Spirifer musebachanus, S. pilosus. Encrinites also occur, and a Cyathophyllum, 
which is too obscure to be determined. The fossils from the outcrops west of San Francisco 
mountain are not well preserved ; indeed their specific characters are so obscured that they can- 
not be determined. One of the specimens is a very large Productus, and is probably a variety 
of P. semireticulatus. Others are fragments of coral, which are too much mutilated to be re- 
cognised. In the notes, January 9, Mr. Marcou states that he found at this place three or four 
beds filled with fossils, the same as at Sandia mountain and the Pecos villages. He enumerates 
Productus semireticulatus and P. punctatus, Spirifere, Terebratule, and Polypi, and says they 
are very abundant and form a lumachelle. Mr. Campbell informs me that the fossils at this 
place and at the Sandia mountain in the cañon of San Antonio are very abundant, and that at 
the latter locality they are found along the roadside, and may be readily knocked out of the 
