118 EXPLOBING EXPEDITION FROM SANTA FE, ETC. 



aptumed edges of the Cretaceous and Triassic rocks; the angle of inclination becom- 

 ing greater as we approached the mountain. Our march afforded us many wild and 

 picturesque views, made so both by the ragged outlines of the hills and the bright 

 colors of the materials composing them; some consisting of blood-red sandstone; 

 others of snow-white gypsum; others still of the two intermingled. 



-Alter winding through a labyrinth of such hills, wo reached the Carboniferous 

 strata, resting directly on the granite. The rocks of this formation are here more cal- 

 careous thanal Santa Fe*, and abound in fossils, among which I saw most of those 

 enumerated in the Santa I-Y section, and, in addition to these, collected a coral and a 

 crinoid, which are apparently new. On descending the eastern slope of the mountain, 

 we found the sedimentary rocks succeeding each other precisely as before. Near the 

 pueblo of Jemez, however, the Cretaceous strata have been entirely removed, but 

 they are visible a few miles farther north. As on the western side, copper occurs 

 h er e near the junction of the Trias with the Cretaceous, [n the valley of Jemez 

 River are a uumber of buttes of white tufaceous rock, representing a geological 

 element of which we had seen QO Iraces in all our explorations of the San Juan coun- 

 try. These buttes are undoubtedly Tertiary, and, as I have stated in my notes on 

 the geology of the vicinity of Ahiquiu, doubtless belong to the great series of fresh- 

 water deposits of Miocene and Pliocene age which skirt the eastern bases of the 

 Rocky Mountains. Here, as elsewhere, they are of local origin and limited extent; 

 having been deposited in ami partially filling an old eroded valley running north 

 and south along the eastern base of Nacimiento Mountain. By the action of Jemez 

 River this valley has again been washed out, leaving only here and there a mass of 

 Tertiary rock standing isolated or adhering unconformably to the sides of the trough 



composed of the older strata. 



"September 26, Jemez to Santo Domingo.— In this part of our route we were almost 



constantly upon the trap mesas which skirt the southern end of the Valles, and 



extend on the east side of the Rio Grande to the Cerillos. This great overflow oi 

 trap, though deeply eroded by the Rio Grande, is geologically quite modern, present- 

 ing the same appearance, in all respects, as the trap plateaus which surround the 

 San Francisco Mountain, Mount Taylor, the Raton, &C; all of which I have before 



described." . 



The r „//„ s ,_x () one- has yet penetrated the Valles to study their geological 



structure but there can be little doubt of its general character. This mountain group 

 is composed of a number of parallel ranges, of but limited extent, having the general 

 trend of all the chains of the Rocky Mountain system of this vicinity, separated by 

 several well-marked, picturesque, and fertile valleys, from which, rather paradoxically, 

 the mountains take their name. While we know that the sedimentary rocks are 

 visible in many places in the Valles, and that the principal axes are granitic, still the 

 presence of immense sheets and masses of trap give an aspect to the scenery ami a 

 character to the geology somewhat differenl from those of most of the mountain regions 

 visited on the present expedition. On the eastern side of the Valles, to and beyond 

 the Rio Grande, nothing but trap is visible; and we here re-entered the region 

 so fully described in a preceding chapter. 



