DEVONIAN—CARBONIFEROUS LIMESTONE AND FOSSILS. 
61 
a metamorphosed clay-slate, which it most probably is. There are no further observations on 
these metamorphic strata except the statement that the trap immediately adjoins the carbon¬ 
iferous limestone. 
Further west, at the cliff of carboniferous rocks, the carboniferous limestone was found to he 
resting on a hand of red sandstone, the thickness of which is not stated. The relative positions 
are shown in the small section given with Mr. Mareou’s notes, January 22. At the point 
where this sandstone was first seen, it was six hundred feet above the trail, in the face of a bluff 
twelve hundred feet high. It was reached beyond this in the course of the survey, and was 
under foot. There are no observations on its thickness or mineral characters. As there does 
not appear to be any good evidence of the Devonian age of this layer of sandstone, and as it 
occurs at only one place, and even there in a comparatively unimportant extent, it has not 
received a separate coloring on the map and section, but is included with the carboniferous 
limestone. 
CARBONIFEROUS. 
Before the expedition of Lieutenant Whipple, our knowledge of the position and mineral 
characters of the carboniferous formation along the line of the thirty-fifth parallel was very 
slight, and did not equal the extent of our information respecting these rocks further north 
along a region less known to civilization. 
The existence of thick beds of limestone in the mountains along the Rio Grande was early made 
known, but no collections of the included fossils were made and brought in. Dr. Wislizenus 
reported them as Silurian, and mentions the strata as occurring at several points along his 
route southward along the valley of the Rio Grande. Lieutenant Abert, who visited one of the 
mines in the Gold mountains, found it to be in limestone, and procured a Terebratula from the 
rock which he has figured in his report. 1 
At the north, the collections made by Colonel Fremont and Captain Stansbury had demon¬ 
strated the existence of the carboniferous limestone as far west as the shores and islands of 
Great Salt lake. 
The collections made by Mr. Marcou when with Lieutenant Whipple, leave us no longer in 
doubt with respect to the age of the limestones of the Santa Fe and Albuquerque or Sandia 
mountains, their Carboniferous age is clearly established, and the formation is also shown to 
extend westward of those ranges as far as the Aztec mountains, in longitude 113°. The rock at 
each of these localities is charged with the fossils characteristic of the carboniferous or mountain 
limestone, and it is associated with thick beds -of sandstone and shales, corresponding to the 
coal-measures of other districts. The formation was also observed at other localities, as has 
been shown in the chapter on the geology of the route ; and as a particular description of the 
observations at each locality is there presented, it is only necessary here to compare these obser¬ 
vations, and to present some of the general conclusions which maybe drawn from them. 
Carboniferous limestone .—The general descriptions have already shown the occurrence of the 
carboniferous limestone at the following places along the line : At Delaware mountain, Santa 
Fe and Albuquerque mountains, Sierra Madre, and west of San Francisco volcano, in the Aztec 
range. 
Lithological characters .—The several outcrops of limestone differ somewhat in color and 
general appearance ; but this difference is chiefly found between the rock of Delaware mountain 
and those further west, which more nearly agree in their color and general aspect, judging from 
the descriptions and the fossils. The only specimen brought in is from Delaware mountain, 
(No. 59 of the catalogue and description,) and presents a very light-grey or yellowish-grey 
color, different from the bluish-grey tint of the fossils from the Pecos villages, and west of San 
Francisco volcano. 
The limestone of the Albuquerque mountains, according to Mr. Marcou’s notes, is greyish- 
1 Report of an Examination in New Mexico. 
