RESUME OF LITERATURE. 131 



scheme, their lithologic and other characters do not agree. Bed 12, which Hohnes 

 believes to be the same as Newberry's bone bed, invites comparison with the Dolores 

 formation, which also is bone-bearing, but the thickness is widely different. Simi- 

 larly the white sandstone, which is Holmes's bed 13, resembles the La Plata sand- 

 stone, but they differ widely in thickness, and if correlated the bone bed would occur 

 above the division in one case and below it in the other. Probably the Lower 

 Dakota and the laminated bone bed combined are equivalent to the McElmo forma- 

 tion, the white and pink sandstone to the La Plata, and the red massive sandstone 

 to the Dolores. 



The distribution of these beds is described bj- Holmes as follows: 



"The areas occupied by Juratrias and Carboniferous rocks call for nothing more 

 than a mere mention, as thej' are quite limited in extent, incomplete in exposures, 

 and totally without fossil remains. In the La Plata ]VIountains there are exposures 

 both of Red Beds and of Carboniferous sandstones; but the}' are to a great extent 

 metamorj^hosed beyond recognition. About the sources of Bear River there are also 

 exposures of the rocks of these ages, but I was not able to examine them. In 

 Dolores Canyon, in the McElmo at the north base of Ute Peak, in the Montezuma 

 Canyon, and on the Lower San Juan, there are slight exposures of the purple 

 laminated beds and of the pink and red sandstones. On three sides of the Carriso 

 Mountains there are outcrops of the Red Beds, but these are mostly bej'ond our dis- 

 trict. From the summits of the Carriso Mountains I obtained a comprehensive view 

 of the tract of countr}' about the valleys of Gothic Creek and the Rio de Chelly; 

 nothing but red and white sandstones appear. A white or slightly pinkish sandstone 

 is in this section peculiar to the upper part of the heav}^ sandstones of the Juratrias." 



Under the title of "The geology and vein structure of southwestern Colorado," 

 Comstock treats of an extensive area which includes the San Juan region." The 

 sandstones cropping out near the Animas Canyon this author refers to the Upper 

 Silurian, and the Ouray limestone he makes Devonian. The Carboniferous is divided 

 by him into an Eo- and a later Carboniferous series. The former, consisting of argil- 

 laceous, calcareous, and arenaceous beds with a thickness of 1,300 feet, is probably 

 the exact equivalent of Cross's Hermosa formation. He remarks (page 227): "On 

 Hayden's map thej are marked Middle Carboniferous; but I can not find any good 

 reason for this, and I suspect that we have here the I'epresentatives of both the 

 Lower Carboniferous and Middle Carboniferous of other portions of the Rockj^ 

 Mountains.", In this, of course, he is undoubtedly in error, as the Ouray limestone 

 represents the Lower Carboniferous, as the term is used and the beds generally 

 identified, by the Haj^len survey. Producius semistriatus, Athyris mitilita, and 

 Sjjirifii' sp. are cited from this bed, the fauna apparently being borrowed from 

 Endlich's account in the Hayden annual reports.* Under the term Later Carbon- 

 iferous, he includes some 2,000 feet of red sandstone which probably is about 



a Am. Inst. Mih. Engrs., Trans., vol. 15, 1887, pp. 218-265. 



'>U. S. Geol. Geog. Surv. Terr., [Eighth] Ann. Kept., for 1874, 1876, p. 216. 



