MANNER OF DEPOSITION. 103 



except in the dolomite, and the smithsonite is the principal zinc ore in the 

 limestone. 



Po§epny'3 conclusions. — It is not necessary to give a detailed description of 

 the specimens of zinc ore from which Posepny concludes that these de- 

 posits are pseudormorphs after limestone. Suffice it to say that the zinc 

 minerals have very often precisely the same structure as the original lime- 

 stone, and that many pieces have been found in which the thin veins of 

 calcite in that rock are continued in the form of smithsonite in the adjoin- 

 ing zinc ore. In some few places in the mineral zone the galena-blende 

 deposits have undergone decomposition, and galena, blende, and calamine 

 are found together. Posepny gives the priority of formation to the 

 galena-blende deposits, as at some points where decomposition has taken 

 place and a portion of the ore has been removed part of the space has 

 been filled with calamine. He further says that the calamine is probably 

 the product of the decomposition of the blende, and that the zinc deposits 

 themselves were formed by the substitution of zinc carbonate for calcium 

 carbonate. From the fact that the galena-blende and the zinc deposits in 

 Raibl are formed each in a different manner, this author regards it as prob- 

 able that in the regions of Upper Silesia, Belgium, and Sardinia, where 

 these two kinds of ore occur in the same deposits, they owe their origin to 

 the same different causes which brought about their deposition in Raibl. 



Comparison of Raibl and Eureka. AltllOUgll the Elll'eka Ol'eS do UOt COlltaill d 



very large amount of zinc, either as blende, calamine, or smithsonite, yet 

 numerous specimens of calamine have been found in the oxidized ores which 

 exactly correspond with the pseudomorphs after limestone which Posepny 

 describes, and which were evidently formed directly or indirectly by sub- 

 stitution for limestone. Whether the zinc was originally substituted for 

 the limestone as blende, and afterwards oxidized to calamine, or whether it 

 was oxidized first and in the form of a solution attacked the limestone, is 

 uncertain, but it is probable that it was deposited as silicate from a solution, 

 as examples of other secondary minerals in the form of stalactites and sta- 

 lagmites are not uncommon in druses in the oxidized ore bodies. The infer- 

 ences which Posepny draws regarding the deposits of Upper Silesia, etc, 

 from those of Raibl, are certainly not applicable to the Eureka ores. 



