198 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



remainder of the immense thickness of siinihir and apparently conformable 

 slates.^ 



The Knoxvilleand Mariposa series. TllOUgll the bcd.S of tllO KnOXvllle and Mari- 



posa gronps, which on the strnctural and paleontolog-ical grounds already 

 stated are considered as of the same age, appear to have a very wide distri- 

 bution in California, particularly along the two great mineral belts of the 

 State, they have been found fossiliferons at only a com])aratively small 

 number of localities in Lake, CVdnsa, Yolo, Napa, Solano, Contra Costa, 

 Santa Clara, San Luis Obispo, and Mariposa Counties. Owing to the ex- 

 tremely disturbed and liigldy metamorphosed condition of the greater part 

 of the series, all of these localities are of very restricted area. The areas 

 covered by unaltered or very slightly altered rock s apparently of the same 

 age are considerably larger, yet even these are small and seem to represent 

 mere patches Avhich by accidents of structure liave escaj;ed the general 

 and very intense metamorphism. The features presented by the rocks of 

 these series as a whole are somewhat unusual among beds so recent, and 

 their general facies has led some able and experienced geologists to suspect 

 for them a far greater antiquity than is warranted by tlie detailed evidence. 

 Though in some of the fossil localities shells are extremely abundant, 

 sometimes making up a large portion of particular strata, the number of 

 species found is small, and of the short list which can be enumerated many 

 are so imperfect as to make their identification doubtful or hopeless." The 

 following were published by Mr. ({abb: 



Belcmnites iinjtreiisus Gabb. Liocium punctatKin (labb. 



Pala'cttracfus crasuKS Gabb. . Modiola major Gabb. 



Cordiera mitra'formls Gabb. AnceUa Piochil Gabb. 



Airesius lirafits Gabb. RhynvhoneUa Whitnei/i Gabb. 



Bingiiiella polita Gabb. Pecten compkxicosta Gabb. 



'Mr. J. Marcou stated tbat these schists "sont souvent tres rapprochds des veiues nidtallifi'ies, 

 sans tontefois jamais en renfernier" (Bnll. Soc. g^ologique France, 1883, p. 410). He now accepts 

 without objection my statement that gold quartz veins occur between the slates of the Mariposa beds, 

 and not simply near them. It does not follow, ho thinks, that because the Mariposa beds, which in his 

 opinion are Triassic, form an integral portion of the auriferous series, the apparition of gold in the 

 Sierra Nevada is to be put as late as the Jurassic. Thi.^i, in his oijinion, took place not later than the 

 Lower Paleozoic. " The extrication of gold from the quartz matrix being due to pressure, naturally 

 gold dust entombed in the Tiiassic marl of the Mariposa may have been united into small nuggets dur- 

 ing the process of lamination and crushing" (American Geological Classification etc., 1888, p. 'St), I 

 must confess myself unable to follow this reasoning. 



''The paleoutoldgic.al st.atements are all on the authority of Dr. White and are in part extracted 

 verbatim from Bull. U. S. Gaol. Survey No. 15. 



