SYSTEMATIC PETROGRAPHY 487 



one of the great German masters, almost at the close of the 

 century. 



Rosenbusch's primary division of rocks is into four great 

 classes : 



I. Eruptive rocks (" Eruptivgesteine "). 

 II. Stratified rocks ("Die schichtigen Gesteine "). 

 III. Crystalline schists. 

 III. Primary crust of the earth (" Erste Erstarrungskruste "). 



Concerning the first class, it is to be noted that Rosenbusch 

 drops the term " massig," used for twenty-five years, as less 

 appropriate — " weniger passend villeicht " — than Eruptive. In 

 the further treatment of eruptive rocks Rosenbusch does not 

 depart from the principles and methods of the last edition of the 

 " Physiographie derniassigen Gestei?ie^ and there is, therefore, no 

 occasion to repeat the analysis of that work already given. 



The stratified rocks of Rosenbusch form a class under the general 

 idea expressed by Lossen. It is pointed out by Rosenbusch 

 that the character of the materials of stratified rocks is not so 

 intimately related to the essence (" Wesen") of the mass as with 

 eruptive rocks, and hence there is no corresponding firm basis 

 for their classification. 



Stratified rocks are divided into seven families, as follows : 



1. Precipitates — including rock salt, gypsum, anhydrite, barite, etc. 



2. Psephites and Psammites or clastic rocks. 



3. Siliceous rocks — not clastic, partly chemical deposits, partly organic, 

 partly of undetermined origin, e. g., lydite, diatomaceous earth, sinter, etc. 



4. Carbonate rocks — including limestone, dolomite, and impure calcare- 

 ous rocks, loess, etc. 



5. Iron rocks — including spathic iron, spherosiderite, brown hematite, 

 bog ore, etc. 



6. Clay rocks — including clay, clay-slate, phyllite, etc. 



7. Porphyroid. 

 Appendix. Coals, etc. 



In this arrangement Rosenbusch attempts no logical con- 

 struction of anything which can be called a system. As he 

 frankly admits, the porphyroids are metamorphic rocks, often 

 associated with the crystalline schists, and as they were not 



