1(U) CARUONIFEROUS FORMATIONS AND FAl'NAS OF COLORADO. 



whicli lies licncath th(> Ordoviciaii limestone in x'ctidn r soiilli of (ho Arkansas. 

 Endlich ajiiiMrcntly regards them as the same. This fact and tlie ajipareiit ahseiieo 

 of tlie Sawatch in Kndlich's sections north of the river lead me to consider it possi)>le 

 that he may have mistaken the position of the heds, and that the quartzite really 

 occurs beneath instead of upon the Yule. In that case the Parting formation as a 

 quartzite would he wanting at stations 53 and 56, and the sections at Fossil Ridge 

 and on the south side of the Arkansas would be in closer agreement with those made 

 there. Along with the Sawatch and Yule, the Parting formation, probably as the 

 result of Paleozoic erosion, seems to l)e wanting over the Sangre do Cristo region 

 in all but its northernmost portion, though possibly' it ma}' be found in fragments 

 associated with them in occurrences such as the Van Diests have made known in the 

 vicinity of Trinchera Peak on the west side of the range. 



In the San Juan region it seems to me iDrobable that the Parting quartzite will 

 prove to be represented by the middle or shaly member of the threefold Devonian 

 series of Cross and Spencer, the two lower divisions of which are recognized by 

 them as possibl}' pre-Devonian. This shale in the San Juan region, which has a 

 thickness of about 50 feet, occupies a position with regard to the Ouray limestone 

 similar to that which the upper or shal}' member of the Yule limestone holds to the 

 Leadville limestone in the Crested Butte distiict. This portion of the Yule, which 

 measures 6<» to 90 feet in thickness, Spurr believes to be the same as the Parting 

 quartzite of the Aspen and Leadville sections. Spurr found iish remains of 

 Devonian type in the Parting quartzite at Aspen. Somewliat similar ones occur in 

 the middle or calcareous member of the Yule limestone at Crested Butte, while 

 Endlich cites them from the middle or shaly division of Cross and Spencer's 

 Devonian. While positive proof is lacking, it seems to me that a number of circum- 

 stances favor the correlation of these shales in the Crested Butte district and San Juan 

 region. The absence of the calcareous and tvpical Yule limestone in the latter area 

 shows an independence of distribution which would seem to justity the separation of 

 the upper from the middle divisions of that series made bj Spurr. Its correlation 

 with the Aspen section and position in the time scale, however, are cjuestious apart, 

 and I am indisposed to accejDt the evidence for the Devonian age of this horizon as 

 conclusive. 



The Parting quartzite Was included by Stevenson in the Silurian, to which he 

 referred all the sedimentaries below the Carboniferous limestone, and the practice 

 of the Hayden survey appears to have been the same. Emmons, as we have alreadj' 

 seen, refers it to the Silurian in his Leadville work. Eldridge, in the Crested Butte 

 district, includes what, according to Spurr, is an equivalent body, as the upper division 

 of his Yule limestone. Spurr recognized the Parting quartzite at Aspen, but, on the 

 strength of some fish remains of Devonian type, assigns the formation to that period. 



