Mesozoic and Cmnozoic Geology and Paleontology. 31 



found Jurassic fossils, in the beds above, which ave referred to Juras- 

 sic age, it left the conclusion with him that the red sandstones are of 

 Triassic age. The credit, however, of first announcing the age of these 

 sandstones is due to M. Jules Marcou, who, as early as 1853, in his 

 "geological map," etc., "with an explanatory- text," referred the 

 beds of conglomerate, described by Capt. Stansbury, in the environs 

 of the Devil's Gate, Rocky Mountains, and the conglomerate and sand- 

 stone described by Prof. Dana, on the Shaste river, and the boundary 

 between Oregon and California, to the Trias. The reader may also be 

 referred to his " Resume and Field Notes," in Vol. 3, Pacific R. R. Sur- 

 ve3% where he identified these rocks at numerous places near the 35th 

 parallel. 



Dr. Peale found a section of Jurassic rocks, at the head of Second 

 Canon, Eagle river, about 940 feet in thickness, and consisting of 

 marls, sandstones and limestones. Another on Roaring Fork below 

 station No. 14, 440 feet thick, and another in the lower Canon of Gun- 

 nison river, near station GO, representing 242 feet in thickness. It oc- 

 curs usuall}' only as a narrow belt outcropping beneath the Dakota 

 Group. 



In 1877, Arnold Hague* estimated the thickness of the Triassic on 

 the outlying ridges and foot hills of the east side of the Colorado 

 Range at 800 feet. The group is found immediately overl^dug the 

 Coal Measures all along the foot-hills of the range, the continuitj^ of 

 the out crop being broken in only a few places, and in most cases, 

 simply by being concealed below the uncomformable Tertiary beds. 

 The rocks are characterized hy a prevailing brilliant red color, which 

 shades off into j^ellowish and whitish tints, and, near the top and bot- 

 tom of the series, show frequently reddish-gray bands. The deep brick- 

 red color, however, is so persistent as to form one of the most clearly- 

 defined geological horizons of the uplifted sedimentary beds. 



The group reaches its greatest development to the southward in 

 Colorado, between the Big Thompson and Cache la Poudre, while north 

 of the railroad it appears much thinner, and, between Lodge Pole and 

 Horse Creek, reaches its minimum. Still farther to the northward, in 

 the region of the Chugwater, it again thickens, but scarcely attains 

 the thickness in Colorado. A section at Chugwater shows between 500 

 and 600 feet of strata, and another at Box Elder Creek, G50 feet. 

 Sandstones form by far the greater part of the entire series of strata. 

 Even the conglomerates, shales, clays and earthy beds, which occur in- 



'■■= Geo. Expl. 40th Parallel. 



