AURIFEROUS GRAVELS—INDEPENDENCE HILL FLORA 89 1 



Liocardiion apicinum Cpr. Galerus sp. 



Fusiis (Exilia) sp. 



Independently, however, of this flora and fauna the strati- 

 graphic evidence connecting the lone formation with the ante- 

 volcanic bench gravels is positively and unmistakably indicated, 

 and the two can at numerous points be shown to run over one 

 into another ; thus south and north of Rocklin, Placer county, and 

 at the mouth of the Yuba as well as north and south of the area 

 here specially treated. As the bench gravels, the lone forma- 

 tion is overlain by rhyolitic and andesitic tuffaceous beds. 



Age of the rhyolitic tuffs and associated gravels. — These are but 

 slightly younger than the bench gravels, but no flora has been 

 studied from them unless that of the Chalk Bluffs be partly from 

 that horizon. 



Age of the gravels of the iiitervolcanic erosion period. — Leaves 

 have been collected by Diller from Monte Cristo gravel mine, 

 Spanish Peak, Plumas county, which are from a bed overlain by 

 andesite and, according to Turner, pretty certainly later in age 

 than the white quartz gravels, although not positively repre- 

 senting the period of the andesitic flows.' In Mohawk Valley 

 Turner has collected leaves from the Neocene lake beds con- 

 taining rhyolitic fragments and covered by andesitic tuffs. 

 According to Professor Knowlton^ these are closely related to 

 the flora of the auriferous gravels. The leaves from Tuolumne 

 Table Mountain are also, according to Turner, later than the 

 auriferous gravels proper. 



Among the localities described by Professor Whitney is 

 Bowen's tunnel. Placer county, two miles north of Michigan 

 Bluffs. Regarding this place. Professor Whitney writes, using 

 the notes of Goodyear (Auriferous Gravels, p. 93). "The 

 gravel averages a foot or two in the middle of the channel. 

 Over the gravel is first a mass of 'chocolate'" (a brown con- 

 solidated clay, probably a volcanic mud) "from one to four feet 

 in thickness; above this is the gray cement" (andesitic tuff) 



^Am. Jour. Sci., June 1895. 



^Fourteenth Ann. Rep., U. S. G. S., p. 466. 



