TAENCLASSIFICATION OF THE [IGNEOUS ROCKS 9 
furnished by the interesting types, Toscanite, Vulsinite, and Cim- 
inite, recently described by Washington.t They form together 
an intermediate family connecting the trachytes with the andes- 
ites, and called by Washington, trachy-dolerite, though it seems 
to me trachy-andesite is to be preferred. Trachy-dolerite- 
ciminite, or trachy-andesite-ciminite, is a term which tells at 
once that the rock to which it applies is a species of trachy- 
andesite which has been described from Monte Cimino. The 
term latite proposed by Ransome? for this group, while other- 
wise appropriate, fails to show the family relationships. Van 
Hise? has already suggested such a compounding of terms to 
express relationships. Certainly if the nomenclature of the 
science is to aid rather than to distract the worker some such 
reform from present conditions is demanded. 
Graphical methods essential to a comprehensive study of rock 
analyses—TVhe necessity for studying the chemical composition 
in connection with the mineral composition of a rock requires 
that we examine in connection with one another the chemical 
analyses of all rocks having the same mineral constituents; or, 
better, those having the same constituents in the same relative 
quantities to a rough approximation. Such analyses show varia- 
tions of one, two, or more per cent. in the quantities of some of 
the constituents for a single species or variety. But, on the 
other hand, differences of one or two per cent. in the amount of 
a constituent may be the cause of important differences in 
mineral composition or in other characteristics of the rock; hence 
it is important to know to that degree of precision the amount 
of each constituent which is present. For each analysis that 
would be remembered, it is necessary, then, to keep in the mind 
eight numbers of one or two figures each; and the student of 
petrology who would be familiar with the chemical nature of any 
tH. S. WASHINGTON: Italian Petrological Sketches, No. 5, JouR. GEOL., V, 
PP- 349-377; 1897. 
?F, LESLIE RANSOME: Some Lava Flows of the Western Slope of the Sierra 
Nevada, Cal., Am. Jour. Sci. (4), V, p. 373, 1898. 
3C. R. VAN HisE: The Naming of Rocks, Jour. GEOL., VII, pp, 691-693, 1899. 
