JUEASSIC. 559 



The McElmo beds of Dry Valley are fossiliferous, locally at least, as proved by Newberry, 

 who found saurian bones in place at about 500 feet below the Dakota in the southeastern 

 branch of Dry Valley, named by him Canon Pintado or Painted Canyon. From Newberry's 

 description of the locality and our own observations of the Canon Pintado from the mesa to 

 the west, as well as on the route traversed through Dry Valley, it is certain that the saurian 

 bones came from the McElmo. Newberry expressed no positive opinion as to the age of the 

 bone-bearing horizon, but called it "Jurassic (?)" in his "General section of the valley of the 

 Colorado." 



The saurian bones found by Newberry were described by Cope as the type of Dystrophxus 

 vixmalx, and were said in positive but quite unwarrantable terms to have come from the Trias- 

 sic, with no suggestion of the provisional assignment to the Jurassic by Newberry. Cope states 

 that Newberry excavated the bones of Dystrophseus "from the red and green rocks usually 

 referred to the Trias, hence from the same formation which yielded the Typothorax already 

 described." The Typothorax in question was found in New Mexico with belodont crocodile 

 and other forms, almost demonstrating that its horizon is the fossiliferous zone of the Dolores 

 Triassic formation, the place of which in the Grand River section is nearly or quite 1,000 feet 

 below the McElmo beds, as will be shown in a later section. Cope adds emphasis to his error 

 as follows: "More than usual interest attaches to this fossil. It is the iirst one found in the 

 Triassic beds of the Rocky Mountain region. * * * The rock is described by Prof. New- 

 berry as the same as that ■s'fhich I have identified in New Mexico as the Trias and is of the usual 

 red color." In harmony with the occurrence of Dystrophseus visemalx in the McElmo beds it 

 has recently been pointed out by F. von Huene that its affinities are Jurassic rather than 

 Triassic. 



That the McElmo beds contain vertebi'ate fauna of the " Atlantasaurus beds" of Marsh 

 has been demonstrated by Riggs, who discovered many dinosaurian remains in that formation 

 near the junction of the Grand and Gunnison rivers at the northeastern base of the Uncom- 

 pahgre Plateau. While this vertebrate fauna has not as yet been described, it is referred to by 

 Riggs as clearly the same which characterizes the Jurassic beds of Wyoming and the eastern 

 base of the Front Range in Colorado. It is said that "representatives of a single genus (Moro- 

 saurus) have been observed to range through the entire series," meaning a section some 500 or 

 600 feet in tliickness below the Dakota. * * * 



The term La Plata formation has been applied in the San Juan folios and other publica- 

 tions to the lower part of what Eldridge described as the Gunnison formation. 



The La Plata consists of two massive sandstone members with an intermediate member 

 of more thinly bedded sandstones and a variable amount of bluish fresh- water limestone. The 

 sandstones are commonly not indurated, as in the Elk Mountains; instead they are rather 

 friable and crumbling, although of homogeneous texture. Cross-bedding is a marked feature, 

 and not infrequently a massive ledge as much as 100 feet in thickness has no prominent divi- 

 sion planes. Of the two sandstone members the. lower is commonly the thicker and much 

 more massive than the upper. The latter is in fact occasionally thin bedded and shaly and 

 may be inconspicuous. 



The calcareous member is very variable in character. On the San Miguel River, in the 

 Telluride quadrangle, it is in some places a pure massive blue-gray limestone in several beds 

 and with almost no shale. Usually dark calcareous and bituminous shales and thin-bedded 

 sandstones, with more or less of massive limestone, occur between the two main sandstones 

 and sometimes reach a thickness of nearly 100 feet. 



The total thickness of the La Plata formation varies, in the area we have examined, from 

 about 100 feet in the Ouray and TeUuride quadrangles to 500 or more in the La Plata Moun- 

 tains, and it is known that to the west all members increase still further in thickness. 



The sandstones are almost whoUy quartzose, and their normal color adjacent to the San 

 Juan Mountains is white or gray, -.but yellow, orange, or red tints have been observed in that 

 region. The cement is often calcite. 



