SMS GAM AIMG PETEROGRA PAY, 359 
and mas) they, are of ditterent modes of origin, there can be 
no species comparable to those of plants, animals, or minerals, 
and hence a classification, properly speaking, is an impossibility. 
Reviewing the various characters of rocks as to their application 
in nomenclature and description, this author touches on some 
fundamental points with noteworthy discrimination. This is par- 
ticularly true with regard to his remarks on the availability of 
texture for purposes of classification. Noting that it is the most 
easily distinguished character of rocks, and that it had been 
used as a primary factor in classification, he pointed out that 
chemical and mineral composition were more fundamental, and 
that there was nothing so intrinsically important in texture that 
differences in that respect should be allowed to separate things 
otherwise alike.t It seemed to him better to name the rock 
from its mineral composition, and for textural varieties to add 
expressive terms. 
In this first edition of the Gesteinslehre, von Cotta introduced 
no geological factor into his adopted arrangement. He treated 
all rocks in the following groups, which were purely for con- 
venience : 
1. Basaltgesteine. g. Kalksteine und Dolomite. 
2. Griinsteine und Melaphyre. Io. Gypsgesteine. 
3. Trachyte. 11. Verschiedene Mineralien als Ges- 
4. Porphyre. teine. 
5. Granite und Gneisse. 12, Eisengesteine. 
6. Glimmerschiefer. 13. Kohlen. 
7. Thongesteine. 14. Triimmergesteine. 
8. Kieselgesteine. 
In the second edition of the Gesteznslehre, issued in 1862, 
while still claiming rocks to be incapable of true classification 
by inherent characters, von Cotta makes a noteworthy advance 
toward a systematic arrangement by grouping them primarily 
according to geological mode of origin. As further factors he 
uses, in certain classes, broad chemical distinctions and form of 
occurrence. His general scheme is as follows: 
™ Genau genommen ist indessen die Textur gar nichts so wesentliches, dass sie 
veranlassen konnte, wegen ihrer Ungleichheit zwei Gesteine ungleich zu nennen, 
wenn sie tibriges gleich sind.”—Gesteznslehre, p. 22, 1855. 
