GEOLOGY OF THE SIERRA NEVADA. 



39 



W 



gold is known to be of Secondary age, and no proof has been obtained of 

 the existence of any member of the geological series other than this. 



When we seek to determine what part of the Secondary is represented in 

 the auriferous slate series ; or which of the numerous divisions or groups of 

 the Secondary or Mesozoic series can be recognized in the Sierra gold-bearing 

 formations, we find that the data are far from sufficient to enable us to arrive 

 at any satisfactory conclusions. That no part of these rocks is Cretaceous, 

 is known from strati graphical evidence ; the rocks of this age occur on the 

 Hanks of the Sierra in such a way, that we have no difficulty in assuring our- 

 selves that they do not make up any part of the auriferous series, 

 must therefore admit that this latter is either of Triassic or Jurassic age, or 

 that it includes more or less of strata belonging to both these periods. 



Here it is desirable to introduce a few words in regard to the known 

 occurrence of Triassic rocks on the west slope of the Sierra, as well as in other 

 localities on the Pacific side of the Continent and in the Great Basin. The first 

 discovery of this group of strata was made by the Geological Survey, in 1862, 

 at various points in the Washoe Mining District, near what is now known 

 as Virginia City, and also in the Humboldt Eanges and elsewhere in Nevada. 

 The same formation was also recognized in Plumas County, California, in the 

 course of the Survey explorations of the year 1863. Numerous discoveries 

 of Triassic fossils have been made since that time in the State of Nevada, but 

 no other one within the borders of California. The only locality of these 

 fossils thus far discovered on the western slope of the Sierra is the one in 

 Plumas County, mentioned in Geology I., p. 309, although a most careful 

 search has been made by the members of the Geological Survey during sev- 

 eral seasons of field-work not only in Plumas, but in all the other mining 

 counties. The area over which these fossils were found in Genesee Valley 

 is extremely limited ; but a sufficient number of species were obtained, to 

 make it clear that the formation was the same which has proved so prolific 

 in a portion of Western Nevada, and especially in the Humboldt Ranges, and 

 which has been traced to the north as far as the Aleutian Islands* This 

 group of rocks, so extensively developed on the Pacific coast, is the exact 

 equivalent of the Alpine Trias, or the beds of St. Cassian and Hallstadtf It is 



\ 



* See Palaeontology of California, Vol. I. p. 19. Report of the Fortieth Parallel Survey, Vol. IV. 

 P- 99. Voyages a la Cote Nord-Ouest de PAmirique, par A. L. Pinart, Vol. I. Pt. 1, p. 34. 



t Mr. Meek remark* (in the fourth volume of the Fortieth Parallel Survey Report, p. 8): "It is a 

 ^inarkable fact that there should be at these distant western localities an immense series of deposits, con 



