68 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



productive in the overlying millstone grit and slate. With the exception 

 that the fissures themselves are not often ore-bearing and that almost all 

 signs of stratification have been obliterated in Eureka, there are strong 

 points of resemblance between the Nevada deposits and those of Cumber- 

 land and Derbyshire. The galena in the English ores" never contains over 

 S37.70 (0.1 per cent.) of silver to the ton of 2,0(J0 pounds, and it is usually 

 poorer. It is not often accompanied by blende or pyrite. Fluorite and 

 barite, as well as calcite, are common; but quartz is seldom found. 



Deposits of Westphalia. — The ore deposits of Eureka resemble those of West- 

 phalia 6 in a few respects. The ore in the latter locality is found in irregu- 

 lar masses, which are all more or less connected with fissures or breaks as- 

 sociated with slates and limestone. It occurs only in the limestone and 

 never in the slate, and it is evident that in both regions the nature of the 

 country rock has had an immediate effect upon the deposition of the ore. 



Deposits of upper silesia. — The deposits of Upper Silesia, c in which calaminn 

 is the prevailing ore, although they have some points in common with those 

 of Eureka, are, on account of difference in structure and variety of mine- 

 rals, more widely removed from them than most of the lead deposits. 



Deposits of Raibi. — The deposits of Raibl, in Carinthia, so fully described by 

 Posepii5', d have considerable similarity to those of Eureka, and although 

 they are principally interesting on account of the bearing they have upon 

 the theory of substitution of ore for limestone, yet a general description of 

 them may be found useful here, as showing some physical characteristics 

 which they have in common with those of Eureka. According to this 

 author the deposits are found in a thick belt of ore-bearing limestone 

 (erzfiihrender Kalkstein), which overlies a calcareous tufa and underlies 

 slate on the southern slope of the Alps. The strata pitch gently to the 

 south. The upper portion of this ore-bearing limestone is more or less 

 magnesian, and contains here and there layers of dolomite slate. The 

 ore deposits are found concentrated on the hanging-wall side of these 



"Henwood on Metalliferous Deposits ami Subterranean Temperatures, Part I., pp. 10S and 109. 

 'v. Cotta: Erzlagerstatten, II., p. 133. 



"Pietch, Zeitschr. fur Berg, Hiitten u. Salinenwesen, B. 21, 1873, p. 292. 



^F. Posepn£ : Die Blei-undGalmei-Erzlagerstatten von Raibl in Karnten. Jabrb. der k. k. geolog. 

 Reicbs-Anstalt, Wien, 1873, B. XXIII. 



