56 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



Of the existence of the Devonian, which is recognized in theWasiitch 

 section, and which was also found by Mr. Walcott in the Kanab, in the Colo- 

 rado Plateau country, no direct evidence was found in the Mosquito region. 

 On the one hand there is a gap of two hundred feet or more of beds from 

 which no fossils were obtained, between the horizons in which Carboniferous 

 and Silurian forms, respectively, were recognized. On the other hand, at 

 one point evidence of non-conformity by erosion was observed between the 

 Blue Limestone or base of the Carboniferous and the Parting Quartzite or 

 top of the Silurian. Had this evidence of erosion been generally observed 

 throughout the region, it would have aftbrded sufficientl)^ conclusive proof 

 that, owing to a perhaps local elevation, no sediments had been deposited 

 here during tiie Devonian period. As it is, the question must remain for the 

 present undecided, though the probabilities are in favor of the latter so- 

 lution. 



As to the existence or non-existence of the Devonian on the eastern 

 slopes of the Rocky Mountains in general, the evidence is equally unsatis- 

 factory. Waverly forms, which ai-e associated with it in the Wasatch, 

 have been found in the limestones of Lake Valley, in New Mexico. It is 

 indicated on the Hayden maps as occurring on the south slopes of the San 

 Juan ■Mountains, and Dr. Endlich's description of the formations in the 

 neighborhood of the Animas River would seem to indicate the existence of 

 a considerable thickness of beds below the Carboniferous which are not 

 like the Silurian or Caml)rian formations of Colorado in general. Unfor- 

 tunately the fossil {Rhyuconella EndJichi ^) upon which he mainly founded 

 his determination of the existence of Devonian beds in the region, has, upon 

 recent, more careful study by Prof. R. P. Whitfield, been decided to be a 

 Carboniferous and not a Devonian type. 



' Geological aud Geographical Survey of the Territories, 1874, p. 213. 



