128 A. W. Jackson — Nomenclature of Crystalline Rocks. 



the duty of each to express his ideas in the form of a classifica- 

 tion, just so strongly would I insist upon the duty of each to 

 refrain from u>':\j. a name in a different sense from that in 

 which it was originally proposed, or from that which is already 



In selecting a nomenclature, that one should be chosen which 

 is embodied in a convenient form accessible to all, which is 

 freest from inconsistencies, and which has already attained the 

 widest recognition. No American author, nor English, nor 

 French can pretend to claim that his names are autl 

 even in his own country. Germany if not the mother is at least 

 the foster-mother of petrography and the literature of every 

 other country is small compared' with her own. In Germany 

 two men— Zirkel and Rosenbusch— have won the highest re- 

 cou-nition for tli :ir co trib 'ions to this branch of geology. 

 Zirkel's "Lehrbuch der Petrographie " (1866) while still the 

 best for field petrography is already too old to represent the 

 present condition of the science. Of more recent works, Zir- 

 kel's "Mikroskopische Beschafh ien and Ge- 

 steine" (1873) and Rosenbusch's "Mikroskopische Physiogra- 

 phie der massigen Gesteine" (1877) are most worthy of being 

 cited. The latter is later and goes more systematically over 

 the entire field. I think Rosenbusch's names are better chosen 

 and capable of better defense than Zirkel^. where they differ. 

 1 shall follow Rosenbusch in the series ol papers which 1 pro- 

 pose to present to the Academy of S « nc< - <> '< '. ifbruia on the 

 rocks of the Pacific coast. 



Summary. 



Permanence of rock-names is desirable ; hence names should 

 not be dependent in any manner upon the system of rock -clas- 

 sification, for classifications change. 



The names of rocks should be uniform, i. e., used in the same 

 sense by all geologists ; they should be stable, i. a, not subject 

 to change; they should be adaptable, i. e., to the somewhat 

 variable nature of each rock. 



In forming rock names both facts and theories offer them- 

 selves as determining elements. The latter should be rejected 

 as they admit of honest differences of opinion. Of facts, we 

 have chemical, ^colopiea.1 am! mineral, /ical at our disposal. 



Both chemical and geological facts should be rejected in de- 

 termining rock-names, because mineralogical (and textural) 

 differences among massive crystalline rocks can be adeqnately 



ami where such differences do not exist, it is undesirable to 

 have names based upon geological or slight chemical differences. 



