'i(l'2 CAKIiONU'KKdl'S l.'oliMATTONS AND FAUNAS OK COLOKADv'). 



(liuiinutitm ii\ tliickncss ol' these strata as they pass eastward is due to the absence of 

 iiuTi-asiTii;- uiiiounts of sedniient, probably the effect of erosion. That this agency 

 had a doiiiinaiit share in reducing- the Mississippian (Leadvillej limestone to its 

 present dinuMisions I have no doubt; wiiilc tlic fact that the series along the Front 

 Range, wliidi tin- larliiM' geologists thought to he unbrolcen and complete, has been 

 shown, as work increased in detail and relinement, to be juost incomplete and 

 interrupted, lends color to .such an explanation for the whole. 



It is indeed possible that another interruption or unconformity occurs within 

 the Upper Carboniferous. The thinning of the upper Wasatch from 5,400 feet 

 in the Wasatch Mountains to lOO feet (Weber limestone), for in.stance, in the Crested 

 Butte quadrangle, would indicate, if not actual erosion, at least .somewhat excep- 

 tionally unequal deposition, while the overlap of the Maroon beds upon the granite 

 is not without significance. Variation in the lower Maroon, as elsewhere dis- 

 cussed, has led to a somewhat similar suspicion relative to the division Ijetween it 

 and the upper member. It also appears to me highly probable that an interruj^tion 

 in sedimentation, if not actual erosion, intervened between the Maroon series and 

 the Triassic above it. 



From the evidence at hand it seems impossible not to accept the correlation by 

 Emmons and King of the Uinta .sandstone and the Weber quartzite. The correlation 

 of the Weber quartzite of Utah and the Maroon formation of Coloi'ado, thus suggested 

 by a comparison of the geologic sect-ions of the two areas, seems to be partially 

 expressed by Emmons in emplo3'ing the term Weber formation for the lower half of 

 the series which, in the Tenmile and Leadville districts, represents the original 

 Maroon formation. It is the AVeber quartzite of Utah and the Maroon formation of 

 Colorado that in approaching each other are supposed to pass into the Uinta sand- 

 stone. One point of difference is the red color of the typical Maroon and the general 

 whitish tint of the Weber quartzite. However, the Maroon seems to lose most of its 

 color in the Leadville and Tenmile districts, while the eastern exposures of the Uinta 

 sandstone have the brownish tint which is supposed to characterize it. 



Since the Weber and Maroon foi-mations maintain so uniform a thickness (from 

 4,000 to 6,000 feet) both in Utah and Colorado, it is a matter of surprise that the 

 Uinta sandstone should I'each a thickness of 12,000 feet and more, and the first 

 inference would be that the Uinta sandstone represents something more than these 

 formations. It can, however, hardly represent the whole Paleozoic series of Colorado. 



The differences existing Vjetween the Uinta sandstone and the varied sediments 

 of the different Paleozoic horizons of Colorado are differences both of character and 

 of thickness. If the supposition be entertained that the Uinta sandstone represents 

 the entire Paleozoic series of Colorado, the differences of character become more 

 pronounced; if only the Maroon formation, differences of thickness. The former 



