Notice of Syenitic Rocks from California. — Turner. 377 
In a recent paper by Weed and Pirrson * the following 
occurs : 
It seems to us that the time has come when a sharp distinction 
must be drawn between the general terms in use by field geologists, such 
as granite, porphyry, trap, greenstone, etc., and the more exact and de- 
finite nomenclature demanded by the needs of petrology. Such terms 
have a definite and proper value just as tree, bush, and vine have in 
botany, but the science of petrology demands at present a terminology 
which will not only be qualitative but quantitative in its meaning. 
While it is neither possible nor desirable to classify rocks on a strictly 
chemical basis, it is clearly evident that the lines of mineral and conse- 
quently of chemical variation must be more strictly drawn than has 
heretofore been done. This will find its natural manifestation in ;i 
more strict regard to the relative quantities of the various minerals 
which are present and these quantities within reasonable limits must 
be expressed. 
Professor Brogger \ has recently suggested a scheme of 
grouping of rocks in which the quantitative chemical ami 
mineral composition is taken into account more narrowly than 
usual. In this way of grouping all rocks of approximately 
the same mineral and chemical composition are brought to- 
gether in families without regard to their structure, age, or 
the mode of their occurrence. Thus the granite family of 
Brogger will include granite, granite-porphyry, and rhyolite, 
and the diorite family (medium acid plagioclase rocks) both 
diorite and andesite. This method of grouping the rocks seems 
to the writer most desirable, and is essentially followed also 
by Levy and Teall and some other petrographers. A rough 
sketch of such a classification, in so far as it applies to the 
rocks studied by the writer in the Sierra Nevada, is herewith 
appended. This is obviously very incomplete, and moreover 
contains practically nothing original. 
The feldspars are the main basis of classification in the 
feldspathic rocks. The ferromagnesian elements offer a con- 
venient means of distinguishing the rock species. 
Granite Family,— alkali feldspar and quartz. 
Granite, — structure hypidiomorphic or granitic. 
Biotite-granite. 
Hornblende-granite. 
Augite-granite. 
Granulite, Levy (Aplite, Rosenbusch), — structure granulitic. 
Granite-porphyry (Microgranite, Levy in part). 
*Am. Jour. Sci., 3, vol. l, 1895, p. 478. 
tDie Gesteine der Grorudit Tinguait-Serie ; Christiana. 1894, p. 92. 
Die Eruption sfolge der triadischen Eruptivegesteine bei Piedazzo in 
Sudtyrol, 1895, p. CO. 
