SYSTEMATIC PETROGRAPHY 453 



that they exerted a controlling influence over the usage of a 

 multitude of workers. 



Ferdinand Zirke I, 1873. — In 1873 appeared Die mikroskopische 

 Be sclia ffenlieit der Mineralien u?id Gesteine, by F. Zirkel. The 

 systematic point of view occupied by this authority at this time 

 is expressed in the following tabular analysis of his larger 

 divisions of rocks : 



A. Non-clastic rocks (" Nicht-klastische Gesteine " ). 

 I. Simple ( " Einfach " ). 



II. Composite ( " Gemengt " ). 



1. Massive ( "Massig"). 



a. Feldspathic ( " Feldspath-haltig " ). 



b. Non-feldspathic ( " Feldspath-frei " ). 



2. Schistose (" Schieferig"). 



B. Clastic-secondary rocks ( " Klastische-deuterogene-Gesteine " ). 



Comparing this scheme with that of the Lchrbuch der Petro- 

 graphie, we find that the microscope has convinced Zirkel that 

 crystalline cannot be appropriately opposed to clastic. He also 

 believes that origi?ial cannot be used for non-clastic rocks because 

 they have been discovered to be at the present time in part 

 composed of alteration products. He therefore falls back 

 on a negative term, nonclastic, admitting that it is indefinite — 

 "misslich." Massive is defined as not schistose, in larger part 

 granular — "nicht geschiefert, zum grossen Theil kornig." 



The work deals mainly with the feldspathic, massive, composite y 

 fton-clastic rocks. These are subdivided as follows : 



I. Orthoclase rocks. 



1. With quartz. 



2. Without quartz, with or without plagioclase. 



3. Without quartz, with nephelite ( or leucite). 

 II. Plagioclase rocks. 



1. With hornblende. 



2. With augite. 



3. With diallage. 



4. With hypersthene. 



5. With mica. 



6. With olivine. 



III. Nephelite rocks. 



IV. Leucite rocks. 



