524 C. P. BERKEY — STRATIGRAPHY OF THE UINTA MOUNTAINS 



their former level. Later erosion has removed 15,000 

 to 20,000 feet of this and redeposited it along the 

 flanks and in adjacent basins forming all the later 

 rocks. 



Unconformity 



An erosion unconformity occurs in the upper car- 

 boniferous beds in this western Uinta region. Evi- 

 dence is not readily detected along the usual lines 

 of travel, but in no less than four somewhat out- 

 of-the-way places the break is well marked. It 

 may be seen in the vicinity of the forks of the Du 

 Chesne river, just above the massive and cherty 

 limestone member, and is succeeded by the last 

 heavy third quartzite formation of the Paleozoic 

 series. The conglomerate was noted on Farm creek, 

 Rock creek, and Rhodes plateau. Where best ex- 

 posed, at the headwaters of Farm creek, the upper 

 margin of the gray limestone is very uneven and 

 carries a great quantity of chert— often more than 

 50 per cent of the whole rock. In addition to the 

 unevenness of this formation, whose billowy out- 

 line is not followed by the overlying laminations, 

 the two are not everywhere conformable in angle. 

 There is discrepancy in dip and strike of the two 

 beds, the limestone being more steeply inclined and 

 less uniform. 



The base of the overlying formation, chiefly 

 quartzite, is a true basal conglomerate. There are 

 abundant fragments and pebbles and boulders from 

 the cherty limestone bed immediately below, and 

 in some places the finer cementing or filling matter 

 is calcareous rock flour (calcilutyte) and granular 

 limestone (calcarenyte) and chert (silicarenyte). 



Fossils are very abundant below the break, but 

 rare above it in this area. From the above it is cer- 

 tain that there is an erosion unconformity in the 

 Upper Carboniferous of the Uintas that marks a 

 moderate readjustment of levels, so that the strata 

 are not perfectly conformable in angle, although 

 the later folding of the range has been so much more 

 profound that this is lost sight of except along the 



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