356 On the Pamgenetic Relations of Minerals, 



Among the carbonites belonging to this formation may be 

 named, as most important, pearl-spar, the lightest of the so- 

 called brown spars, and tautokin, characterised by its far great- 

 er density. It is much to be desired that these two minerals, 

 so interesting as regards the geognosy of lodes, should be ex- 

 amined chemically. The analyses of brown spars are indeed 

 numerous, but in the absence of data for the angles and den- 

 sities, they are comparatively valueless to the mineralogist. 

 When associated with barytite, the former of these minerals 

 is seated under, the latter upon it. Chalybite and some 

 varieties of calcite are likewise frequent associates. On the 

 contrary, witherite, strontite, alstonite, barytocalcite, and 

 neotype occur but rarely, and only in particular limited lo- 

 calities. Pinguite, chloropal, and hyposiderite, must be re- 

 garded as altogether sporadic, and rare productions of recent 

 date. 



Quartz again is frequent, partly as the bedding of the for- 

 mation, more frequently as a subsequent production ; in the 

 latter case constituting a large number of pseudomorphs. 



Even the barytite presents, although rarely, impressions 

 of crystalline minerals immediately antecedent to it, shewing 

 that the formation of barytite was here and there connected 

 with the destruction of previously existing minerals. 



Fluorite and barytite have been decomposed even still more 

 frequently. These two minerals, and likewise the implanted 

 calcite, have been removed, particularly during and still more 

 after the formation of the more recent quartz. Hence origi- 

 nate the extremely numerous quartz and horn stone pseudo- 

 morphs after those minerals. They are partly incrustation, 

 partly replacement pseudomorphs, sometimes both. The 

 numerous tabular impressions in the quartz and galena of 

 Andreasberg (Harz) shew clearly that barytite once existed 

 there in great quantity, although at the present time not a 

 particle is to be found, and baryta occurs there only in the 

 hornstone of the more recent zeolite formation. In the Kur- 

 pring Friedrich August mine at Freiberg, the barytite has 

 partially disappeared, and pseudomorphous quartz occupies 

 its place. Witherite produced by the alteration of barytite, 

 is of rare occurrence, and in all probability owed its origin, 



