98 The Paragenetic Relations of Minerals. 



These divergent zones frequently contain the same mi- 

 nerals as the above-mentioned masses and the primitive 

 limestone. In the divergent zones of cobalt glance in very 

 quartzy gneiss at Skutterud (Norway), a brown phengite mica 

 occurs in a very characteristic manner. It is, however, less 

 abundant in those parts of the zone containing amphibole, 

 which is chiefly associated with arsenical pyrites. It is not 

 an improbable conjecture that these deposits of cobalt glance 

 were formerly lodes containing spathic iron, spies cobalt, iron 

 and arsenical pyrites, which in the general metamorphism 

 were converted into magnetite, cobalt glance, and tesseral 

 pyrites. A number of instances prove that in metamorphic 

 rocks amphibole is very abundantly associated with the more 

 ferruginous minerals — a circumstance to which Durocher has 

 specially drawn attention.* 



These zones are sometimes interrupted apparently as 

 though the substance of the pre-existing lodes had collected 

 together in masses during the metamorphism. The deposits 

 of magnetite in Scandinavia present these characters, and at 

 Arendal they contain phrenite and datolite minerals, which 

 otherwise occur only in lodes and vesicular cavities. It is 

 likewise probable that the deposits of copper pyrites and 

 galena in Scandinavia belong to this class, as well as deposits 

 of pyrites, blende, and garnet, in the Upper Erzgebirge, the 

 Banat Servia. &c, which present great analogies to those of 

 Scandinavia. 



for the opinion that there are two kinds, the one giving rise to the production 

 of definite minerals, the other consisting in an alteration, more or less complete, 

 of such minerals into suhstances which are not strictly speaking mineral species. 

 In the former process, although thermic agency may occupy an important place, 

 it is perhaps more advisable to apply to it the term plutonic, which admits of 

 a wider signification. The latter process, in which water appears to be a prin- 

 cipal agent, takes place chiefly in limestone rocks ; those consisting essentially 

 of amphfbole and felsite (dioritic), and those consisting of pyroxene and felsite 

 (greenstones) producing pseudomorphous hydrated silicates, among which, as re- 

 gards frequency, serpentine takes the first place; then follow pyrallolite, praslite, 

 gigantolite, aspasiolite, phastine, and all the ophitic substances. Most of the 

 asbestus occurring in veins in serpentine and diorite, was most probably at some 

 period amphibole or pyroxene. 



* Etudes sur lc metamorphisme des roches. Bulletin de la Societe Geol. de 

 France, 2 C scr., torn. iii. 



