336 Tlie Paragenetic Relations of Minerals. 



more recent than it ; but, as Nbrdenskjold first pointed 

 out, they never occur without beryl. It cannot therefore be 

 doubted that their presence depends upon the pre-existence 

 of beryl. 



Iron pyrites, arsenical pyrites, galena, and zinc blende — 

 the most frequent minerals in the Freiberg lodes, impregnate 

 the adjoining gneiss to a distance of several fathoms. Al- 

 though the walls of the lode fissures presented an abundant 

 surface for their deposition, a considerable transfer of these 

 substances from the lodes into the adjoining rock is some- 

 times unquestionable, and in this case the rock is generally 

 disintegrated. Frequently the mispikel occurs imbedded in 

 the gneiss, at a distance of 15 to 20 feet from the lode, in 

 such quantity as to be advantageously worked. The gneiss 

 is then converted into talc, or a very analogous substance. 



The occurrence of calcite, both imbedded and in small 

 veins, in the zechstein of Saalfeld, is a phenomenon which 

 should probably be included among the above. 



It may not be inappropriate here to make some mention of 

 the artificial crystals obtained in smelting processes. The 

 beautiful homogeneous and vitreous slags, from Hockeroda 

 and Luisenthal, contain tabular, tetragonal-prismatic crys- 

 tals, of a substance closely resembling idocrase, both imbed- 

 ded and forming druses, in the larger vesicular cavities. 

 Hexagonal-prismatic crystals, resembling nepheline, occur in 

 the same manner in the slag from the Rothenthal at Osterode 

 (Harz). 



4. Some imbedded minerals are undoubtedly products of 

 the decomposition of the mass in which they are inclosed, 

 and are therefore more recent than it. 



In the brown coal of Artern (Thuringia), mellite and sul- 

 phur occur in separate crystals and groups. At Luschetz 

 (Bohemia), mellite and oxalite occur in a similar manner. 

 Bischof considers that the carbonaceous matter of the coal 

 lias reduced sulphate of lime, and that subsequent contact 

 of the sulphuret with sulphuric acid, resulting from the oxi- 

 dation of pyrites has reproduced gypsum, with evolution of 

 sulphuretted hydrogen, which, with oxygen, yielded water 

 and sulphur. However, the sulphur in the brown coal of 



