On the Paragenetic Relations of Minerals. 143 



moreover, intersected by porphyry, while this formation in- 

 tersects porphyry. Assuming the porphyry to be of the same 

 date, this would support the opinion of miners who regard 

 the formations as different. Still there are no grounds for di- 

 viding the pyritic lead and zinc formation into so many parts 

 as Werner did. On the other hand, it cannot be doubted 

 that there are several formations of galena and zinc-blende, 

 for instance, the clinoedritic and the barytic. But these 

 two minerals frequently occur together elsewhere without 

 any recognisable relations to other minerals as regards date 

 having yet been ascertained, therefore the possible future ne- 

 cessity for further subdivision must not be altogether denied. 

 The zinc-blende is almost always the black variety, especially 

 when associated with arsenical pyrites, and indeed whenever 

 pyritic minerals preponderate. When.it is of a brown or red 

 colour there is seldom much if any pyrites near. It is well 

 known that black zinc-blende contains an essential admixture 

 of sulphuret of iron, and has a lower specific gravity than that 

 of any other colour. 



The clineodritic lead and zinc formation sometimes di- 

 rectly follows the present one ; however they must neverthe- 

 less be regarded as distinct. 



Sometimes the heavy spar formation is likewise present with 

 and without the noble quartz ores, which are, however, less 

 abundant the greater the quantity of pyritic minerals, and 

 in this case belong to a more recent formation which has been 

 sporadically imbedded in that of the latter, as is the case in 

 the noble quartz formation, where such lode substances are 

 generally absent. 



The pyritic ores are met with, although quite in miniature, 

 in the fissures of argillaceous spherosiderites, the lode veins 

 of coal strata, and even in the cavities of limestone petrifac- 

 tions of still more recent date. 



The minerals constituting this pyritic lead and zinc forma- 

 tion are frequently mixed together in coarse masses, no con- 

 stant succession being observable except in the druses which 

 sometimes occur where the lode bellies out, when galena and 

 zinc-blende present themselves as the older, and pyrites as the 

 younger members. Two generations have likewise been ob- 



