Spur? 1 — Quartz-muscovite rock from Belmont, Nevada. 357 



These schists strike north and south parallel to the beresite 

 dikes; the} 7 often contain serpentine. The beresite had been 

 so named by the miners of the district previous to Rose's 

 investigation, and had been hunted for as the surest index to 

 gold. The dikes are cut obliquely by highly inclined or ver- 

 tical auriferous quartz veins. Ordinarily these veins do not 

 extend beyond the beresite, but sometimes they enter the 

 country-rock, and even extend to the next dike. The beresite 

 itself, where it consists chiefly of quartz,' muscovite and pyrite, 

 notably near the river Tcheremchanka, contains, according to 

 the researches of A. Sokolow, 50 drachms of gold to the ton. 

 Rarely, native gold has been found in it.* A peculiarity of 

 the beresite, which makes it difficult of investigation, is its 

 profound decomposition, fresh portions being very rarely met 

 with. In the upper horizons it is often altered to a light col- 

 ored clayey mass, while the neighboring schists of the country- 

 rock are altered to a red clay. 



After the thorough description of beresite by Rose no other 

 studies were made until Karpinsky published his results in 

 18T6.f Karpinsky investigated what appeared to him to be 

 fresh pieces of the beresite, and these showed themselves to be 

 free from feldspar and to be composed of muscovite and quartz, 

 with a little iron-pyrite. He came to the conclusion that the 

 beresite is a feldspar-free rock, and, contrary to Rose's opinion, 

 not to be connected with granite. In his second paper, Kar- 

 pinsky admitted that orthoclase is present in beresite from 

 another locality, and separated the rock into a feldspar-free 

 and a feldspar-bearing variety, which are connected with one 

 another by transitions. Besides the beresites at Beresovsk, a 

 number of other Russian localities have been described by 

 Rose,;}; while Karpinsky and Arzruni§ have added still others. 



What appears to be the most thorough and clear-sighted 

 study of the beresite was made in 1885 by Arzruni.| He 

 describes the beresite as a fine-grained dike-rock of coarser or- 

 finer texture and often semi-porphyritic structure, the varieties 

 of this rock being so varied in their peculiarities that it seems 

 proper to describe the different occurrences separately. By the 

 diminishing of one or the other of the mineral constituents, 

 such as the feldspar or the mica, special types are presented. 



* A. Karpinsky, Guide des Excursions du VII Congres Geologique Interna- 

 tional, No. 5, p. 41. 



f Protocol of the Geologic-Mineralogic section of the Natural Science Society at 

 St. Petersburg meeting on the 3d of May, 1875, and on the 9th of September, 

 1876. German summary of the Russian text given by Arzruni, Zeitschr. d. 

 Deutsch. Geolog. Gesell., vol. xxxvii, 1885, p. 867. 



% Reise, etc., vol. i, pp. 294, 302, 321, 436 ; vol. ii, pp. 34, 36, and 557. 



§ Zeitschr. d. Deutsch. Geolog. Gesell., vol. xxxvii, 1885, p. 870. 



| Op. cit., pp. 865-896. 



