RESUME OF LITERATURE. 75 



Yule limestone. No. 3, which is said to be calcareous at one point, may represent 

 the middle division of the Yule, but the upper division, that which Eldridge men- 

 tions as being especiallj' j)ersistent, and which Spurr correlates with the Parting 

 quartzite, appears to have no equivalent in Stevenson's section, unless No. 3 repre- 

 sents it, instead of the middle division. The surprising variability of these beds as 

 described by Stevenson half leads one to doubt the accuracj' with which thej^ were 

 identified at different points, in view of the rapidity with which the work must have 

 been carried on. Stevenson's beds 1 and 2 seem to have no representatives in the 

 Crested Butte section on the scale of the comparisons which have just been made. 

 It seems more likely, therefore, that the varied series described by Stevenson is 

 really only the Sawatch quartzite." It is significant also that he in no instance 

 describes beds which have the character and position of the Yule limestone. 



The different beds mentioned by Stevenson suggest some of those described by 

 Endlich in the San Luis district, but a detailed comparison would not be profitable. 

 If the whole of Stevenson's section represents the Sawatch quartzite, a parallel to the 

 calcareous and shal3' portion (No. 3) seems to be cited by Endlich, who says (page 

 308) that sometimes the quartzites at the base of his section are represented by 

 calcareous ))eds. 



Stevenson gives two sections of the Carboniferous in the Elk Mountains, one 

 near the head of Rock Creek (page 363), which I take to be the Rock Creek on the 

 west side of the Elk Mountains, having its sources near Sopris Peak, and the other 

 at the head of the West t'ork of Taylor River. The relation of the Carboniferous 

 beds at the latter locality to the Silurian section is not given, whether it follows 

 directly or with an interval between. 



The three beds of limestone at the base, aggregating 140 feet in thickness, are 

 with little doubt the Leadville limestone, while the shale above it has the position 

 and many of the characters of the Weber formation as described in the Anthracite- 

 Crested Butte folio. With the conglomerate, just above, the Maroon formation 

 probably begins. Above the 100 feet of conglomerate and sandstone which are 

 supposed to form the base of the Maroon conglomerate there follows an interval of 

 unknown extent, which is succeeded b^^ the section near the head of Rock Creek 

 previously mentioned. '' This interval is occupied principally b}- coarse sand- 

 stones. ..." The Rock Creek section consists of sandstones, thin limestones, and 

 some shale. The thickness, aside from beds 16-25, which are Cretaceous (page 365), 

 amounts to 1,475 feet, but as there is a repetition in the Cretaceous beds, there may 

 be one, though it is not obvious, in the Carbonifei'ous also. All these strata belong 

 evidently to the Maroon formation. 



a In this area the Maroon formation sometimes rests upon the Archean and occupies the position of the Sawatch 

 quartzite. It is possible that an occurrence of this sort may have introduced a complication into this discussion. 



