150 CARBONIFEROUS FORMATIONS AND FAUNAS OF COLORADO 



the noi'thci'ii ciiil 1)1' I he SangTo de Cristo Range. Kndlich describes it in soction r 

 of the San Luis district us a ijrav to bluish limestone with siliceous se^'reofations. 

 characters which apply eijually to the typical Yule of the Crested Butte district or 

 to the \\'hite limestone at Leadville. It rests upon a (juartzite having the characters 

 of the Sawatch quartzite. Except in the vicinity of the Arkansas River neither 

 Endlich nor Stevenson found iinj' Silurian in the Sangre de Cristo region, and in the 

 Haydcn atlas it is represented as missing, the Arkansas sandstone resting innnediately 

 upon the granitic axis of the range. 



In a recent detailed section by Lee, made near Culebra Peak, the older Paleozoics 

 certainly seem to be unrepresented. E. C. and P. H. Van Diest, however, on the west 

 side of the range, at a point nearly opposite Lee's section, in an area in which the Car- 

 boniferous color appears on the Haj'den map, found not the Arkansas sandstone, but 

 beds which appear to belong to the Sawatch and Yule formations. The supposed 

 Silurian rests upon the white Cambrian ( ? ) quartzite separated only hy a thin bed 

 of argillaceous shale, and consists of light graj^ siliceous limestone about 2(>0 feet 

 thick, with others of darker color above." Possibly other isolated occurrences simi- 

 lar to the foregoing will be discovered in the Sangre de (Cristo region. 



Of the Paleozoics of the central Colorado area which lies north of the Eagle 

 and Grand rivers, we know next to nothing except that there seems to be a much 

 greater development of the Cambrian and Ordovician.* 



The section of the Uinta Mountains is lithologically unlike that of the rest of 

 Colorado, and our paleontologic evidence is so incomplete and to a certain extent so 

 contradictory that it will be useless to look there for the Yule limestone or a repre- 

 sentative of it until better information is at hand. It appears, at least, to be absent 

 in its chai-actei' of a limestone, and should it prove to be represented there, it must be 

 by some as yet undifferentiated portion of the Uinta sandstone. I am not unpre- 

 pared, however, to find that the whole Uinta series is of Carboniferous age. 



Turning now to the Front Range we find the Ordovician section, like the Cam- 

 brian, different from that of the interior of the State. The most complete section is 

 that of the Pikes Peak quadrangle, and 1 will briefl\' recapitulate the formations 

 there found and their characters, before touching upon the other sections. In the 

 Pikes Peak folio,'' Cross recognizes three Ordovician formations — the Manitou lime- 

 stone, the Harding sandstone, and the Fremont limestone. The oldest of these, the 

 Manitou limestone, is a fine-grained pink or reddish dolomite less than 100 feet thick, 

 containing Opliileta, C'amarella, and a few other Ordovician fossils. The Harding 

 sandstone has a maximum thickness of 100 feet and is made up of fine-grained sac- 

 charoidal sandstone in alternating banks of light gra}' and pinkish or variegated colors 



a Colorado Sci. Soc, Proc. vol. 5. 1898, pp. 76-80. 



tPeale, U. S. Geol. Geog. Surv. Terr., [Eighth] Ann. Kept., for 1874, 1876, p. 110. 



cU. S. Geol. SuTT.. Geol. Atlas United States, folio 7. 1894. 



