CARBONIFEROUS-ALBUQUERQUE MOUN TAINS. 
31 
developed further to the north ; indeed, it probably forms a large part of the eastern flank of 
the Santa Fe range. It is known to extend for a long distance south, and it flanks the Organ 
mountains and other ranges on the east of the Rio Grande, these being continuations of the 
Sandia range. 
The outcrop of limestone near Tuerto is directly east of the Sandia or Albuquerque 
mountain, and south of Gold mountain, an elevated mass of granitic and metamorphic rocks. 
This granite, and the limestone just south of it, are several miles to the east and north of the 
northern end of the Sandia range, and these are out of the line of trend of the limestone as it 
was observed near San Antonio, and on the top of the range by Mr. Marcou. So, also, the 
limestone on the east side of the Santa Fe range is far east of the line of trend of the Sandia 
range. If we connect these outcrops together as one line of uplift, we must regard the trend as 
changing suddenly to the northeast. We, however, find that the trend of the Sandia range, if 
prolonged across the Rio Grande, reaches to the southern end of a ridge with the same direction, 
and which appears to he the end of the San Juan mountains. The extension of this uplift of 
the carboniferous in that direction is thus rendered extremely probable, especially as the ranges 
further north impinge upon and cross the Rio Grande in a similar manner. It may, however, 
he found that the Santa Fe, the Gold mountain, and the Sandia outcrop, are parts of one line 
of flexure or uplift. 
It is difficult to understand the exact position of the Carboniferous strata relatively to the 
granitic rocks of Gold mountain, and in the interval between this uplift and the eastern base 
of the Sandia range. When Mr. Marcou was travelling at the base of this range he mentions 
passing from the granite to the outcrop of the limestones, three hundred feet thick, the heads 
of the beds looking to the west, and the dip being from thirty-five to forty degrees east. A 
bluff of this limestone was continually on his right hand for one mile as he passed northwards 
towards San Antonio, where the “ Trias” was found. From this we may presume that the 
road was upon the granite, and indeed this is indicated by the section given, (October 8,) 
where the wagon-road is shown on the granite. Under date of October 9th he mentions that 
the inferior Carboniferous extends as far as Tejera village, “ where, as the Trias, the coal has 
been too much compressed and does not appear.” There the thickness of the Carboniferous is 
stated to be two thousand feet. It would thus appear that he crossed the edges of Carboniferous 
strata which probably consist of sandstones of the coal measures in addition to the limestone, 
the thickness of the latter having been previously given as three hundred feet. The sandstones 
are also referred to under date of October 10th. The limestone near the Gold mountain is 
said to dip east, but for a time I was in much doubt whether it was on the western or eastern 
side of the granite ; but it now appears most probable that it is on the eastern flank, and that 
it dips away from the mountain precisely as from the granite of the Sandia range. 
The occurrence of black shales and strata of sandstone with the limestone, and the fact that 
Mr. Marcou gives the thickness of the limestone at one point as three hundred feet, and at 
another locality, but a few miles distant, and in the same line of trend, he found the thickness 
of the Carboniferous to be two thousand feet, leads me to conclude that the coal measures are 
developed there. He also states, in his Resume, that the coal measures do occur there. I have, 
therefore, represented them upon the map and section. 
We would expect to find these stratified rocks, and especially the limestone, coming to the 
surface on the western slopes of the mountains. They do not, however, appear either at Santa 
Fe or on the Sandia range. We are, therefore, at a loss to decide how to locate the beds in 
the interval between the outcrop on the east of the Rio Grande valley and that on the west. 
Mr. Marcou, in his notes, does not mention the presence of any limestone on the eastern flank 
of the Sierra Madre, but in his Resume he distinctly states that it does so occur, and that it is 
succeeded on the west, or beyond the crest of granite, by another outcrop dipping westward. 
The occurrence of this limestone with the easterly dip from the Sierra Madre permits us to 
conclude that it underlies the whole valley of the Rio Grande, and we should, therefore, find 
