KBSTJME OF LtTERATUKE. 135 



diate beds would necessarily be the equivalent of the Dolores and La Plata forma- 

 tions combined. The massive, brick-red sandstone at the base of Peale's Triassic 

 strongly suggests the Dolores formation, while the massive, light-colored upper 

 portion is like the La Plata, but there is here an intermediate series, while below the 

 beds similar to the Dolores 700 feet of Red Beds are found, which Peale places in the 

 Permian. The total thickness of the Red Beds in the La Sal Mountain region, with 

 the limits taken as above, is 2,300 feet. The Dolores and La Plata formations have 

 a combined thickness of only 1,850 feet. The statement made by Cross and Spencer 

 that the Dolores formation, which is almost 2,000 feet thick in the Animas region, 

 is reduced to scarcely half that amount in the vicinity of the La Sal Mountains," is 

 in a measure offset by this fact, that the La Plata sandstone, which varies from 100 

 to 500 feet in the San Juan region, expands to the northwest, and in the Cai\von and 

 Plateau regions, to two or three times the maximum figure for the San Juan (loc. cit. , 

 p. 7i). Furthermore, though the McElmo formation contains 300 feet in the Rico 

 Mountains, and though Peale assigns to his Jurassic a thickness of 250 feet, 3'et 900 

 feet are said to be found in the region adjacent to the Rico section (loc. cit., p. 66), 

 so that some of the upper beds of Peale's Triassic ma\' go with his Jurassic to form 

 the McElmo formation. 



Peale relates that upon West Creek bed 1 (the upper division of his Permian 

 series) rests upon the granite, and that over large areas his Triassic beds occupy a 

 similar position. The interpretation of these facts whicli is to me the most probable 

 is that the}^ record two distinct episodes of submergence, if, indeed, it be granted 

 that Peale has successfull}' performed the diihcult task of correlating or tracing the 

 variable members of his Red Beds sections. It may prove, however, that the con- 

 glomeratic beds on West Creek which he considers represent the upper member of 

 his Permian are really identical with those producing the Triassic overlap; that there 

 was a single submergence; and that parts of the section have been duplicated. In 

 any event there appears to be a sort of unconformity between Peale's Permian, or at 

 least the upper and larger portion of it, and the beds supposed to represent the 

 Hermosa formation. As previously' mentioned, there is evidence of this also in the 

 fact that the Hermosa in Peale's area is so much thicker than farther east, and that 

 the upper portion carries a somewhat different fauna. These speculations, however, 

 are subject to such varying possibilities that in the absence of accurate stratigraphic 

 tracing or the means for paleontologic correlation they seem almost futile. 



Compai'ing next Peale's section with that exposed in the Crested Butte quad- 

 rangle, it appears that if the lowest limestone of the former is really of Mississippian 

 age, it is the equivalent of the Leadville limestone. The shaly sandstone above the 

 limestone would then represent the Weber combmed with the lower member of the 



aU. S. Geol. Surv., Twenty-first Ann. Rept., pt. 2, 1900. p. 67 



