FAUNAL EVIDENCE AND COKEELATION. 245 



the Weber grit-s formation, carrj'ing- with it probably the Robinson limestone and 

 possibh' the middle Weber, corresponds to the Maroon conglomerate. This corre- 

 spondence is not so close as to be striking, and many departures can easilj' be pointed 

 out; but I feel that we have data very far from full as to the faunas of these formations. 

 A comparison of the faunas of all the formations from which we have any adequate 

 collections can be made b\' consulting the summary tables at the end of this chapter. 



Station 2281 probably is bed 38 in Peale's section No. 18, which was made from 

 the mouth of the canyon of Fourmile Creek westward to Horseshoe Mountain." 

 This locality is in the Leadville district, and the horizon can safelj^ be put at the 

 Weber shales. The fauna also agrees with this identification. 



Station 2288 appears to be that mentioned by Peale on page 242 of the same 

 report. The locality is probably near the Tenmile district. The horizon is rather 

 uncertain, but appears to be the Weber shales, from the stratigraphic evidence, 

 while the fauna itself is too limited to afford a clue. 



The collection from station 2289 is that cited on page 369 of the third volume of 

 the reports of the Wheeler survey.'' The section was made on the forks of Eagle 

 River, a localit}" which I have been unable to identify exactly', but which appears to 

 be not far northwest of the Tenmile district. The horizon is bed 19 of the local sec- 

 tion, whose relations with the standard one are as difficult to ascertain as the position 

 of the localitj' upon the map. As it occurs in the middle of a great sandstone series, 

 I suppose that it comes about on the horizon of the Robinson limestone, just above 

 or just below the division between the Weber grits and the Maroon formation. The 

 fauna is too scant}' to afford evidence on this point. 



As our collections contain no fossils from the Front Range and Sangre de 

 Cristo regions, I will proceed to give the faunal evidence from the San Juan region. 



SAN JUAN REGION. 



A wholly disproportionate amount of matei'ial in our Colorado collections was 

 obtained from the small area of Carboniferous strata exposed in the Rico Mountains 

 and in the valley of the Animas River in the southwestern part of the State. This 

 area is partly covered by the Durango, Rico, Engineer Mountain, Needle Mountains, 

 and Silverton quadrangles, and is shown on sheets 4 and 15 of the Ha3^den atlas of 

 Colorado.'' Most of the material obtained was collected by Whitman Cross, A. C. 

 Spencer, and others associated with them. 



The geologic section in the Rico Mountains has been described b}' Cross and 

 Spencer,*^ but generally, it may be said, with reference to the larger area in which 



" U. S. Geol. Geog. Surv. Terr., [Seventh] Ann. Kept., for 1873, 1874, p. 227. 



I> U. S. Geog. Geol. Snrv. W. 100th Mer,, Rept., vol. 3', 187.5. 



cV. S. Geol. Geog. S\irv. Terr., Geol. Geog. Atlas Colorado, 1877. 



d Geology of the Rico Mountains, Colorado: U. S. Geol. Surv., Twenty-flrst Ann. Rept., pt. 2, pp. 7-165. 



