264 PROCEEDINGS OF THE ACADEMY OP 



fort}' miles to the westward of it, from the latitude of Sierra 

 Amarilla as far south as the road from Santa Fe to Fort Wingate. 



Little of novelty has been added from the first two named re- 

 gions, as they have been previously traversed by competent geol- 

 ogists ; but the last named has remained up to the present time 

 almost unknown. The analysis of the structure of the Sierra 

 Mad re range is believed to indicate that its elevation took place 

 near the close of the period known as Cretaceous No. 4, and that 

 the elevating force was in New Mexico, more powerful at its south- 

 ern extremity than along the middle portions of its line. Another 

 important discovery is the lacustrine character of the triassic beds 

 which form a part of the axis of the range ; indicating the exist- 

 ence of extensive areas of dry land at that period, of which no 

 portion is remaining in the region examined by me, but which may 

 be supposed to be represented by the palaeozoic beds further south 

 and west. A third important point is the determination that the 

 plateau drained by the eastern tributaries of the San Juan River 

 is composed of the sediment of an extensive lake of Eocene age, 

 which was probably at one time of great extent, but whose 

 deposits have been greatly reduced in extent through erosion. 

 The boundaries of this lake to the east and south were determined. 



It is believed that additional light has been thrown on the ques- 

 tion of the age of the Galisteo sandstone ; and that its paleontology 

 has decided definitely that of the Santa Fe marls. The first fossils 

 discovered in the " trias" of the Rocky Mountains, have enabled 

 me to reach more definite conclusions as to its position in the scale 

 of periods. 



The remains of vertebrata obtained from the latter formation 

 are those of fishes and reptiles. The former are rhomboganoid 

 scales of small species which are numerous in the coprolitesof the 

 reptiles ; the latter represent the three orders of Crocodiles, Dino- 

 sauma, and apparently of Sauropterygia. The dinosaurian order 

 is represented by a part of the crown of a tooth of a species of 

 huge size, of the general character of Laelaps. Both faces are 

 convex, the one more so than the other, and the long axis of the 

 crown is curved towards the less convex side. Both cutting edges 

 are sharply and closely crenate denticulate as in Laelaps, Aubly- 

 sodon, etc. ; otherwise the enamel is perfectly smooth. There was 

 not enough of this animal discovered to enable me to identify it. 

 The suspected sauropterygian species is represented by a single 

 vertebra with the centrum slightly depressed, circular section, 

 and about as long as wide. The neurapophysis appears to have 

 been united by suture, although this point is not so clear as de- 

 sirable, and the bases of thediapophysis are very stout, extending 

 the entire length of the upper half of the lateral surface of the 

 centrum. Of the articular faces, one is much more concave than 

 the other. Length of centrum, m. .05 ; width, .057 ; depth, .055. 

 The crocodilian remains consist of a portion of a jawbone with 

 alveoli for four teeth, of a broken vertebra, and a number of dermal- 



