ASrElMTES. 151 



holociystallino, but they retain their trachytic character in spite of having 

 cooled at great depths. I incline to the supposition that, owing to chemical 

 differences in the material of secondary consolidation, a greater change of 

 volume has accompanied this final process in the more recent series than in 

 the earlier one and that the cracked feldspars and the smaller cohesion of 

 the trachyte-like rock are due to this change of volume, ihilk analyses of 

 the younger andesites indicate a slightly more acid composition, hut it 

 would be a matter of great difificidty to separate the cr_vstals of [)rimary 

 and secondary consolidation for analysis. Means of deciding this rpiestion 

 may, however, be devised. 



Should the series of younger andesites discussed above, together with 

 the transitional varieties, prove common on the Pacific slope and, as a rule, 

 distinct from the earlier and denser rocks, these plagioclase rocks might 

 convenientl}' l^e termed asperltcs,^ at least for field purposes, in reference to 

 their trachytic character. If these relations, traced by me at four impor- 

 tant localities and suggested by hasty inspection at other points, are gen- 

 eral, it will only be necessary to substitute the term asperite for trachyte 

 on many of the earlier geological maps of the western United States to 

 represent the facts from a modern point of view. Even if the term asperite 

 does not obtain a permanent place in lithological nomencdature, it cannot 

 be amiss to consider its expediency. The nomenclature of lithology is 

 and must always remain more or less arbitrary. I'hat classification is the 

 best which takes account of the greatest number of natural relations; but 

 no classification can embrace them all. To \n\ mind it is an advantage 

 that the term asperite expresses structural as well as mineralogical distinc- 

 tions, for, though a purely nnneralogical classification of rocks is extremely 

 simple, it ignores many of their properties which are of the utmost interest 

 and importance. That the ultimate classification will be purely mineralog- 

 ical appears to me in the highest degree improbable, nor can I believe that 

 it will be founded solely upon microscopical peculiarities." 



' From asper, rongb, the Latin equivalent of rpaxi-;. 



2 C. W. Giinibel (Sitzungsber.k.bayer. Aliad. Wiss., Muniib, vol. 2, 1S81, pp. 365-36.^) suggested ten- 

 tatively tbat tbe andesitin rocks of Soutb and Central America might be divided iuto two types, one 

 trachytic, tbe other basaltic in habitus. I was not awaio of this suggestion when tbe text was writ- 

 ten. Giirabel's material was meager. In bis specimens of trachytic habitus, corresponding to my as- 

 perites, he found no mica. Tlu; specimens nf bas:iltic habitus nbich he examined imludcd none in 



