BESUME OF LITERATURE. 73 



This series, which is reported as almost identically the same as that north of the 

 canyon, both in thickness and in lithology, allows itself to be correlated with compara- 

 tive ease with the formations recognized in the Crested Butte quadrangle. The 

 Sawatch quartzite, it is clear, is wanting, or, more probably, occurs below the lowest 

 strata described. These consist of 320 feet of light-colored limestone with chert 

 concretions, and they, with little doubt, represent the Yule limestone. The yellow 

 and gray shales next above, which have a thickness of 80 feet, are the equivalent of 

 beds of a similar character which in the Crested Butte quadrangle occur at the top 

 of the Yule limestone, and which, it will be remembered, Spurr correlates with the 

 Parting quartzite. The variegated shales which follow also suggest the upper portion 

 of the Yule limestone, but to so identify them would give this formation an almost 

 excessive thickness. All the succeeding formations, except the last, probably belong 

 to the Leadville limestone. The dark -blue limestone with Carboniferous (?) fossils 

 at least almost certainly does. The age of the fauna is not clearly indicated by the 

 faunal list given bj' Endlich. It is compared, perhaps upon the authority of Meek, 

 with the fauna from Mystic Lake, which is of Mississippian age. On the other 

 hand, the general make-up rather suggests the Devonian fauna of the Ouray lime- 

 stone. The Rliynchonella, "which has a decidedly Devonian aspect," I suspect to 

 be Camarotmchm endlichi. It is now known that both Devonian and Carboniferous 

 faunas are found in the Ouraj' limestone, and it may be that the material collected 

 in this case was a mixture from both horizons. At all events, in the limestone in 

 the Elk Mountains identified with the Leadville limestone, Devonian and Carbon- 

 iferous faunas occur similar to those from the Ouray limestone in the S^n Juan 

 region, and the two formations can evidentlj^ be correlated. The occurrence in the 

 limestone of Fossil Ridge of a fauna suggesting the same horizon, corroborating as 

 it does the indications arising from geographic proximitj' and stratigraphic succes- 

 sion, makes it highly probable that we have a recurrence of thgit very persistent 

 formation. There is, however, much more shale associated with the limestone than 

 is known elsewhere, and the lithologic character of the series seems to be more like 

 that of the Weber limestone. 



The enormous area of Stevenson's survey in 1873 " included portions of the Elk 

 Mountains in Colorado. The Silurian he found to be well represented. I have 

 quoted his description of these rocks at length, but while his remarks incite specula- 

 tion the.y lend little aid toward arriving at a conclusion. He says (page 360) : 



" On Taylor River, at its head and along the west side of Taylor Park, as well 

 as at its southeast corner, the Silurian rocks are well exposed, underlying the 

 Carboniferous. So, also, at the head of Tumichi Creek. Throughout this region it 

 seems to be almost entirely free from limestones, and the sandstones give no evidence 



tiU. S. Geog. Geol, Surv. W. 100th Mer., Kept., vol. 3, 1875, pp. 303-BOl. 



