endlich.] CARBONIFEROUS. 217 



ley of the Animas, at an elevation of 10,460 feet the sedimentary beds 

 are soon reached, beginning with the Devonian. Resting immediately 

 upon it are the Carboniferous strata, beginning again with the lower 

 series of sandstones and shales, in terstrati Bed with limestones. South 

 of Sultan Mountain (station 20, 13,306 feet high), the strata have a 

 southerly dip, both the Devonian and Carboniferous, while the overlying 

 trachyte covers them, nearly horizontally stratified. Proceeding from 

 that ppint to the southwest, toward station 31, it will be observed that 

 the dip changes into # an opposite direction, producing a synclinal fold. 

 Upon reaching the station mentioned, however, it returns to such a posi- 

 tion as to become parallel again with the first. This latter change is due 

 to the influence of the main anticlinal axis that has been discussed 

 above. Engineer Mountain (station 31) is located upon an isolated patch 

 of trachyte superincumbent upon the red Carboniferous sandstones. 

 Although no very marked stratification can be observed in the volcanic 

 rock of that small peak, its direction is indicated by the vertical position 

 of the columns in which the trachyte there weathers. The unconforma- 

 bility between the two is not so marked as farther to the northeast, owing 

 to the fact that the eruptive material is found almost directly on the 

 axis of upheaval., A clearer view of the respective relations can be ob- 

 tained from the accompanying section II. Starting from the northeast, 

 the inetamorphic rocks, a, are found to underlie the sediraentaries. 

 They are covered by Devonian limestones, &, containing numer- 

 ous fragments of corals and Spirifer, analogous to the rock upou 

 which station 48 was located. After that the Lower Carboniferous series 

 sets in, c, composed of yellow to brown sandstones and shales, inter- 

 stratified with beds of limestone, some of which contain Productus semi- 

 strlatus. Heavy beds of the red sandstone, d, follow, showing a very 

 considerable development of that formation. Toward station 20 these 

 are capped for some distance by trachyte, e, running out on the spurs 

 from the main group of mountains. To the north of station 31 a lime- 

 stone occurs above the sandstones, exposed on but a small area, and of 

 no considerable thickness. The absence of characteristic fossils in these 

 strata is very much to be regretted. Criuoids and corals of a decidedly 

 Carboniferous type were found there; but such remains by which their 

 age could have been established definitely were not observed. Strati- 

 graphically they are conformable to the underlying beds. Daring the 

 summer of 1873, I found in the red sandstones composing a large por- 

 tion of the Saugre de Cristo range, near their upper limit, beds of lime- 

 stone that showed the same fossils. I am inclined to believe, therefore, 

 that these two maybe parallel; all the more as I consider the sand- 

 stones of the two regions as being of the same age. Crossing that out- 

 crop of limestones, and proceeding northward toward the head of Bear 

 Creek, we again descend into the region of red sandstone. All along 

 Bear Creek it forms the high slopes on either side' nearly down to the 

 junction with Mineral Creek, dipping off yently to the west. At that 

 point the thickness of the sandstones amounts to about 1,800 feet. Near 

 thejunction, erratic bowlders of the Lower Carboniferous limestones may 

 be found, originating from a small outcrop of those strata on the north 

 side of the creek. While the sedimentaries are thus found in the lower 

 canons, volcanic rocks form all the high points. On Bear Creek, 

 about two miles above the junction, a conglomerate may be observed 

 forming one of the highest strata of the sandstone group. Immediately 

 above it the trachyte begins. By the action of the latter it has become 

 thoroughly baked ; is hard and well cemented. At no other point was 

 a conglomerate observed in the same horizon, and it seems probable, 



