On the Paragenetic Relations of Minerals. 359 



Still the bedding of heavy spar is not always wanting, even 

 at Schneeberg, and then the auriferous and argentiferous 

 minerals are generally associated with it. Calcite has like- 

 wise frequently been decomposed during the formation of 

 quartz, which is often pseudomorphous after it, and these 

 pseudomorphs sometimes present regular twins, in which one 

 primary rhombohedron of quartz is joined parallel to the 

 plane — J R of the calcite crystal. 



Moreover, the lode quartz in this formation is always dif- 

 ferent from the rock quartz, — the latter having a fatty, the 

 former a vitreous lustre ; sometimes also being in the form of 

 amethyst. The presence of quartz older than barytite, as 

 well as the association of quartz in general, distinguishes 

 this group from the previous and following group, from 

 which quartz is entirely absent. 



Group D. — Although very little is known of the occurrence 

 of cobalt and nickel in the rocks of the coal formation, it 

 still appears desirable to call attention to the fact. Cotta 

 states that at the Regenberg (Gotha) asbolan occurs in lodes 

 in carboniferous sandstone, so frequently as to admit of being 

 worked advantageously. 



At Bockwa (Saxony) there was found, a few years since, 

 upon small lodes in the upper pitch coal-seams, erythrine, 

 — a mineral which must always be regarded as a product 

 of decomposition ; and as iron pyrites, copper pyrites, ga- 

 lena, and zinc-blende, likewise occur in lode fissures of the 

 coal-seams of Saxony, it is very probable that this erythrine 

 has originated from some pyritic mineral containing an es- 

 sential admixture of cobalt and arsenic. However insignifi- 

 cant this phenomenon may be, it nevertheless gives a hint as 

 to the date of the formation in question. 



Group E. — The lodes belonging to this group are situated 

 in cupreous slate, and the overlying members of the zech- 

 stein. If greywacke, clay- slate, or granite, lie immediately 

 under the zechstein, cupreous slate and old red sandstone 

 being wanting, the lodes continue productive, although to an 

 inconsiderable distance, in the older rocks. Wheu the lodes 

 bear barytite, they extend to some depth, but are unproduc- 



