PETROGRAPHY 361 



paper Written in 1889 he does not confine the metamorphic 

 action of mountain-movements to sedimentary formations, but 

 in common with Lehmann he regards gneiss, hornblendic 

 schist, and other crystalline schists as eruptive rocks (granite, 

 syenite, diorite) in which planes of schistosity have been 

 developed under the influences of pressure and stretching. 

 Rosenbusch does not believe it possible that the fundamental 

 gneisses and schists could have originated as chemical precipi- 

 tates from a primaeval ocean, or any primaeval mixture of 

 rock-material and superheated water. As he further points 

 out, the idea has been exploded that schistosity is a feature 

 peculiar to Archaean rocks, it may indeed be possessed by 

 young-Tertiary rocks. From the general distribution and 

 stratigraphical position of the "fundamental" series, Rosen- 

 busch concludes that it represents in its deeper horizons the 

 first consolidated crust. He thinks the agreement in the 

 mineralogical composition, as well as the interleaving of the 

 Archaean gneisses and schists with the oldest eruptive rocks, 

 would seem to indicate that the Archsean foliated rocks have 

 at least in part originated from the same magma as deep-seated 

 plutonic rocks. But whereas in the case of the granite-grained 

 bosses of rock there is internal evidence that the minerals had 

 separated from the magma in a definite order according to 

 chemical laws, this is quite lacking in the gneissose and 

 schistose rocks, which rather indicate that consolidation had 

 been controlled by mechanical pressure. 



In chemical respects the crystalline schists agree sometimes 

 with massive eruptive rocks, sometimes with sedimentary 

 rocks, and in all probability they have originated from various 

 rocks, from deep-seated and eruptive masses, from intrusive 

 and superficial eruptive flows, from eruptive tuffs, and from 

 all kinds of stratified deposits. According to Rosenbusch, 

 dynamo-metamorphism is the active principle that produces 

 the banded and finely foliated forms of rock-structure. 



In his Elements of Petrology (1898) Rosenbusch defines the 

 crystalline schists as "eruptive or sedimentary rocks which have 

 been geologically transformed through the essential co-opera- 

 tion of geo-dynamic phenomena." He distinguishes the 

 " fundamental " series as an independent primaeval formation, 

 and describes the younger schists as local facies of different 

 rock-varieties and not confined to any geological epoch. 



Credner and Zirkel take exception to these views in certain 



