38 



THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 





The evidence thus furnished — all of which comes from the Geological Sur- 

 vey — i s satisfactory in this respect, that all the localities mentioned are in the 

 very heart of the gold-mining region; those from which the Amelia, was obtained 

 in considerable numbers in Mariposa County are in the closest proximity to 

 the Great Quartz Vein, and extend along its course for fully twenty miles. 

 In this connection, it must be remembered that not a single fossil to which a 

 Palaeozoic age could by any possibility be assigned has ever been found in 

 the mining counties, from Mariposa to Yuba. The only fossils' older than 

 Triassic which have been discovered to the west of the crest of the Sierra 

 are those of the limestone belt, of which by far the most prominent and the 

 most fossiliferous locality is that at Bass's Ranch, in Shasta County, described 

 in Geology I. The fossils discovered here in abundance are of undoubted 

 Carboniferous age. There is also evidence sufficient to determine the geo- 

 logical position of the limestone belt at Pence's Ranch, eighty miles southeast 

 of Bass's ; at that locality, however, there were but few species found, and 

 the specimens obtained were in a much less perfect state of preservation 

 than those occurring at the more northern locality; they were, however, 

 referred without hesitation to the Carboniferous by Mr. Gabb. Somewhat 

 doubtful traces of fossils of the same age were also obtained in a limestone 

 belt in Genesee Valley, more than fifty miles northeast of Pence's Ranch. 



While there are many outcrops of limestone or marble along the course of the 

 Sierra, from Plumas County to the extreme southeastern end of the range, 

 there has never been a recognizable fossil found in any one of these, so that 

 the identity in geological age of the different outcrops of the limestone in 

 that portion of the Sierra with those farther north, although suspected, can- 

 not be demonstrated. 



The evidence obtained in the heart of the gold region — that is to say, in 



— is sat- 



Along 



* 



the counties where mining for that metal has been chiefly carried on — 

 isfactory in so far as this, that proofs of the Secondary age of a portion at 

 least of the auriferous belt have been obtained at numerous points all the way 

 from Mariposa to Nevada County, a distance of perhaps 150 miles, 

 this whole extent no Palaeozoic fossils have been discovered. If the limestone 

 belt in this region belongs, like that farther north, to the Carboniferous, there 

 is no proof of it; so that it may be said, that there is no evidence of the ex- 

 istence of rocks older than the Carboniferous anywhere on the west slope of 

 the Sierra Nevada; and that, in the principal gold-mining region, a portion 

 at least of the rocks most intimately associated with the occurrence of the 



















