AGE OF THE AEAPAHOE AND DENVER. 219 



of the long-continued volcanic outbursts which the formations thus far 

 mentioned show to have occurred at about the same time in widely 

 separated districts. 



The Ohio Creek and Ruby formations. 111 the area COVered 1>V tile Anthracite slleCt 1 



in the West Elk Mountains, Colorado, occur two formations which are 

 analogous to the Arapahoe and Denver beds. One of these, the Ohio 

 ('reek formation, is known only in two small isolated remnants, resting 

 on an eroded surface of the Laramie. The strata are loose, friable 

 sandstones, grits, and fine conglomerates, and contain unidentifiable plant 

 remains. The conglomerates contain many chert pebbles carrying erinoid 

 stems and other apparently Carboniferous fossils. From this fact it is 

 argued by Mr. R. C. Hills, who personally investigated both the formations 

 in question, that between the Laramie and Ohio Creek epochs there was 

 "•reat erosion, cutting through the entire Cretaceous section, at least. 



In the Ruby Range of the Anthracite sheet is a formation 2,000 feet in 

 thickness, resting with apparent conformity on the Laramie, but consisting 

 almost entirely of andesitic debris, forming tuffs, sandstones, conglomerates, 

 etc., of purplish color, and much indurated in this locality through numerous 

 dikes of igneous rock. The "Ruby formation," as it has been called, has 

 been traced by Mr. R. C. Hills continuously for more than 80 miles to the 

 northward, beyond Grand River, where it decreases in thickness to 300 

 feet. At this point the formation is overlain by the Wasatch Eocene and 

 underlain by "200 feet of soft, white sandstones and yellow clay," below 

 which are the firm, gray sandstones of the Laramie. Mr. Hills suggests a 

 correlation between the soft sandstones and the Ohio Creek beds. No fossils 

 are known in either of the new formations aside from carbonized plant 

 stems. 



It thus appears that in the region between the Gunnison and the Grand 

 rivers there is an extensive formation, consisting, like the Denver beds, of 

 fine andesitic debris, and occupying a position between the Wasatch and 

 the Laramie. The Ohio Creek beds are less distinctly an equivalent of 

 the Arapahoe, the principal evidence in this direction being that while 

 these strata are not definitely known beneath the Ruby series the basal 



■Geologic Atlas of the United States, Anthracite-Crested Butte folio, No. 12, 1895. 



