RESUME OF LITERATURE. 137 



as that suggested for the similar section described in the report for 1875, and it is 

 similarly uncertain. The Lower Dakota of Peale's report may be safely correlated 

 with the Dakota of Cross's and Spencer's Rico Mountains section, and his Jurassic 

 is, in a general way, equivalent to their McElmo formation. Peale gives a gener- 

 alized section of his Jurassic beds, to which a thickness of 200 feet is assigned. 

 At the base is a white sandstone, which ma}^ represent the whole or only a part of 

 the La Plata sandstone. In either case Peale's Jurassic is considerably inferior in 

 thickness to the McElmo formation. 



By analogy with his Carboniferous series of the year previous, part of that for 

 1876 would represent the Hermosa formation and part would belong in the Red 

 Beds. Indeed, in the passage quoted above, he calls attention to the similarity of 

 the soft sandstones and gypsiferous shales forming the top of his Carboniferous to 

 the beds forming the base of the Trias. Probabl}' 700 feet of his Salt Creek section 

 (which in 1875 he called Pei'miau) should go with the Trias (?). The upper portion 

 of his Carboniferous series, therefore, together with his Triassic, and possibly the 

 white sandstone at tlie base of the Jurassic, probably represent the Dolores and 

 La Plata formations. As the Ti'iassic is said to measure 500 to 1,000 feet, possibly a 

 maximum of about 1,700 feet would represent Peale's measurements, and this is not 

 far from the combined thickness of the Dolores and La Plata given bj^ Cross and 

 Spencer, though all these formations appear to vary greatly from point to point. 



Peale's measurements made the year previous are considerably larger. He had 

 then 250 feet of Jurassic and in the Salt Creek section 1,600 feet of Triassic. 



In 1901 Elmer S. Riggs described the Dinosaur beds of the Grand River Valle}'- 

 of Colorado." The section treated by this author consists of so-called M^sozoic strata 

 of this region, which is the vicinity of the Dolores, Grand, and Uncompahgre rivers. 

 The lowest of these beds rest upon granitic rock and are referred to the Trias. The 

 Trias is represented by a massive ledge of reddish sandstone, slightly cross bedded, 

 and weathered in peculiar pinnacle and dome-like shapes. Below this is a softer 

 stratum of vermilion-colored sandy shale, the entire thickness being about 400 feet. 

 These are followed above bj' Jurassic strata, which range from 600 to 700 feet in 

 thickness and admit of four subdivisions. The lower or marine Jura is from 100 to 

 120 feet in thickness, and consists of bluish and grayish gypsum-bearing clays in 

 which thin layers of fine-grained sandstone and nodular ledges of limestone are inter- 

 spersed. The latter are never more than 6 or 8 inches in thickness, and are usually 

 from 3 to 5 in number. In no instance were fossils found in these measures. Above 

 this lower member lies a stratum of greenish shale about 100 feet in thickness, and 

 then a darker zone 40 or 50 feet thick, containing frequent ledges of cross-bedded 

 sandstone, and at the top a series of variegated clays reaching a thickness of 300 or 



a Field Columbian Museum, Publication GO. Geologic series, vol. 1, No. 9, 1901, pp. 207-274. 



