180 (.'AKHONIKJ-niors KORMA'I'IONS and [''MINAS ()!•" C'OlyORADO. 



feet. :uul coiitaiius tlic l\)ll(>wiiiy ('IciiU'iils, I x^oi lining at the base: C'ongloiiierato, 

 \\i(li red saiulstono and rod shale. SOU foet; blue. fosHiliferous limestone, 7 feet; rod 

 siitiio and sandstone. TdO fei't; blur unFossilii'crous limestone, 20 feet expostid; red 

 sandstone and reddisli shale, 300 feet; gray liniestoiio, riehly fossiliferons, loo feet; 

 and redtlisli sandstone holding beds of red shale, 1,800 feet. Tiie upper series is a 

 reddish-brown eouglonieratie sandstone not far from 2,500 feet thiek. Large frag- 

 ments of granite, gneiss, and quartzite prevail, but with these are some of sandstone 

 ami limestone. "This part of the section bears close resemblance to the upper divi- 

 sion of the Carboniferous series seen on the Eagle River of central Colorado."" 

 The entire thickness of this series is 6,200 feet, distinctly greater than at any point 

 at which measurements have elsewhere been made. 



Stevenson's comparison of the upper beds in the Sangre de Cristo with the upper 

 division of the Carboniferous on Eagle River (=the upper Maroon'^) is suggestive, 

 and the two divisions distinguished in the Sangre de Cristo can be compared with 

 the two divisions of the Maroon formation in the Crested Butte district. This is 

 especiallj^ true of the upper division, which measures the same in both areas, 3,500 

 feet. The lower division in the Sangre de Cristo is much thicker. In the San Juan 

 the upper division is reduced to 300 feet (Rico formation) and the lower to 1,800 

 feet (Hermosa formation). In the Dolores River region, however, the upper 

 division appears to be entirelj? absent, while the beds supposed to be equivalent to 

 the lower division have about the same thickness as in the Sangre de Cristo, aggre- 

 gating, according to Peale, 8,500 feet, to which possibly 300 more feet should be 

 added from his Permian series. The fauna found by Lee near the base of Steven- 

 son's lower division distinctly favors its correlation with the Hermosa and lower 

 Maroon series. 



W. T. Lee has recentl}' published a very detailed section embracing about -iOO 

 feet at the bottom of the Arkansas sandstone. It was made on the east side of the 

 range at a point directh' west of Trinidad, near the southern end of a tract having 

 its center at Trinchera Peak, which Endlich mapped as Lower Carboniferous. A 

 horizon about 100 feet above the crystallines contains a well-marked Pennsylvanian 

 fauna, and as no evidence of the Mississippian was found, nor any significant litho- 

 logic changes, there can be little doubt that the lowest beds at this point belong in 

 the Upper Carboniferous. Lithologically the series described bj^ Lee consists of 

 numerous alternations of coarse red grits and sandstones, red and black shales, and 

 limestones. The fauna collected by Lee presents points of individuality, but is 

 distinctly that of the Hermosa formation in distinction from the Rico fauna. 



The Arkansas sandstone for the most part rests directly upon the Archean, the 

 earlier Paleozoics probably having been lost by erosion prior to its deposition. 



n U. S. Geog. Geol. Surv. W. 100th Mer., Kept., vol. 3, Suppl. p. 74. 



