44 CARBONIFEROUS FORMATIONS AND KAUNAS OK COLORADO. 



soMH'wIuit iiili'i'iiiediiitc in thickness, corn'sijondini;- to its intermediate geographic 

 position. 



The Mississippian was so uniformly a limostone-maldng epoch in the area of 

 those Westorn States, of Avhicli the Madison, Wasatch, Ouray, Leadville, Red Wall, 

 and other limestones are evidence, that I woidd hesitate to accept an unsupported 

 correlation which would assign to this epoch sands and conglomei'atos in the ai'ca 

 referred to. I would therefore regard the absence of any limestone series in the 

 Uinta .sandstone as evidence that none of its hed.s can be correlated with the Missis- 

 sippian portion of the Wasatch limestone. If the horizon of the Mississippian 

 Wasatch were conceived as coming below the Uinta sandstone, it is probable that the 

 latter must be taken as the representative of the Weber quartzite, as King supposes. 

 Under this hypothesis it would be necessary to account for the absence of the 13,000 

 feet of Cambrian beds and 7,000 feet of Wasatch limestone, not to include the Ute 

 limestone and Ogden quai'tzite, and for the great thickness of the Uinta sandstone, 

 when its supposed equivalents, the Weber quartzite in Utah and the Maroon- Weber 

 interval in Colorado, amount to only 5,0(J0 or 6,000 feet. In the absence of definite 

 knowledge, however, explanation of both these objections can be made. The upper 

 portion of the Wasatch limestone, in amount 5,400 feet, is of Upper Carboniferous 

 age and is not persistently a limestone. The probable equivalents of these beds in 

 the Oquirrh Mountains contain considerable thicknesses of quartzite, and King 

 instances several beds which in their lateral extension vary in an impoitant manner 

 in the relative proportions of tlie calcareous and siliceous constituents (pp. 142 

 and 143). It is not unthinkable, therefore, that the Penusj^lvanian portion of the 

 Wasatch limestone in passing eastward may lose its calcareous composition and 

 Isecome indistinguishable from the Weber quartzite. The beds would have a 

 combined thickness of from 10,400 to 11,400 feet — not far from that of the Uinta 

 sandstone. 



There can be little doubt that the earliest Pennsylvanian sediments were preceded 

 hy erosion, at all events in Colorado, for in Colorado the Mississippian portion of 

 the Wasatch limestone, which has in Utah a thickness of 1,600 feet, is reduced to 

 400 or 500 feet (Leadville limestone), '' with visible evidence of erosion along its upper 

 plane. In places it has even been completely removed. If the pre-Carboniferous 

 quartzites of the Wasatch section have their equivalent in the Ked Creek quartzite 

 of the Uinta section, and if the Mississippian portion of the Wasatch limestone were 

 removed by erosion and the Pennsylvanian portion joined with the Weber in the 

 manner outlined, the difficulties incident to this hj'pothesis would be in large measure 

 removed. 



If, on the other hand, the horizon of the Mississippian portion of the W^asatch 

 be regarded as coming above the Uinta sandstone, the Red Creek quartzite would 



'(500 feet appears to be about the maximum for this formation, and part uf it is of Devonian age. 



