ENDUCH. j 



CARBONIFEROUS. ' 219 



the gray shales of !Nos. 2 and 3, d, follow, upon which the trachyte of 

 the small plateau rests. From there westward the Carboniferous beds 

 crop out only in the lower country, while the higher shows Cretaceous 

 beds. This is the case also with the region lying north. An interesting 

 case of volcanic intrusion occurs immediately south of station 37, of 

 which section IV will give an idea. As stated above, the station is 

 located on the red sandstones, a, which dip from there in a southerly 

 direction. Descending with them a stratum of trachyte, c, similar to 

 that described from station 36, is found imbedded in them, and after it is 

 crossed the sandstones again appear. Shortly after their first outcrop 

 has been passed, a trachytic dike, d, is reached, ascending nearly verti- 

 cally through the sedimentary beds. From there a small point is 

 ascended, and it will be observed that three other trachyte beds are 

 iDterstratified with the sandstones. Not far from the highest portion of 

 the hill a vertical fault has occurred, displacing the strata for the dis- 

 tance of about twenty to thirty feet. By this means the trachyte has 

 been brought immediately opposite the sandstones. It was noticed 

 that the volcanic beds diminished in thickness toward the south, some 

 of them pinching out almost entirely by the time they reach the opposite 

 side of the hill. A trachytic layer caps the entire series. From these 

 and other instances where intrusion was observed, it would seem that 

 the eruption of that isolated mass of volcanics had been accompanied 

 by considerable dislocation, although the relative position of the latter 

 to the sedimentary beds precludes the probability of their having had 

 any share in the formation of the main anticlinal axis. Whence the 

 intrusive material came is a question that may require more study to 

 answer, but it seems to me, so far as I was able to acquaint myself with 

 the character of the geognosy of that section, that it must have pro- 

 ceeded from station 36. Both from stratigraphical and lithological 

 evidence I am inclined to accept this proposition ; all the more as the 

 mineralogical composition of all the volcanic rocks of that entire group 

 is a remarkably uniform one. 



From the localities just referred to, the Carboniferous formation ex- 

 tends down southward for some distance on the west side of the Ani- 

 mas. All along the river, from some distance above station 39 down to 

 station 40, the lower division of the formation is exposed in the almost 

 vertical bluffs that border the Animas Valley on the west side. Litho- 

 logically the strata show the same characteristics that are exhibited on 

 the east side, and are, regarding the vertical distribution of beds, iden- 

 tical with them. Beginning again below with the series of yellow to 

 brown shales and sandstones, the bluffs rise to a relative elevation of 

 1,400 to 1,800 feet above the valley. Toward the top limestones set in, 

 containing some fossils. This formation extends westward and runs 

 for some distance in a line approximately parallel to the course of ttie 

 Animas. It is soon, however, covered by the red sandstones. A num- 

 ber of mineral springs, alkaline, and containing some iron, rise in the 

 lower division. One of them is situated opposite Animas City, near the 

 top of the bluff. Two more are found in the valley near the lower end 

 of Animas Park, starting at the base of the bluff. While the one is 

 cold, the other, but a short distance from it, is warm. A deposit, in 

 part calcareous, has been formed near them. 



Eesting upon these Lower Carboniferous beds we again find the red 

 sandstone, occupying, with reference to the former, the same position as 

 on the east side of Animas. Although there may probably be some 

 variation in the thickness of the beds, increasing as we go westward, it is 

 not of any great extent. A large area is covered by these red sand- 



