400 The American Geologist. -^^^^^ '^^^^■ 
system is expansive for increasing refinement and yet the num- 
ber of terms for a given rank or division is limited. 
3. Nomenclature. This is particularly strong in such terms 
as salic, femic, etc., and in the mnemonic terminations indicat- 
ing classes, ranks, etc. 
4. Suggestive of new lines of investigation. The new 
grouping will stimulate a study of the model variations of a 
given form. It forces home the chemical composition and its 
mineralogical expression and emphasizes the complementary 
roles of rock-forming minerals, it will develop more careful 
descriptive work. 
II. Weak points in the classification. 
1. Nomenclature. There is little connection between the 
field terms proposed and those of the new classification and 
thev are based in some degree on different principles. The 
roots chosen, while adaptable to the specialists of today, have 
little or no meaning or arrangement for the new student or lay- 
man in petrography. 
2. Subordination of texture. The new classification lays 
too little stress on the textures, which are easily recognizable. 
3. Previous literature is rendered unavailable for a number 
of years until it has been thoroughly reworked and rephrased. 
4. Chemical analyses. 
(a) Little can be told with certainty regarding the classifi- 
catory position from an inscription of a chemical analysis and 
no rock is surely placed without going through the entire com- 
putation. 
(b) The increaised refinement in the discrimination between 
bulk analyses surpasses the ability to discriminate types in the 
field. This leads possibly to incorrect geological and petro- 
graphical interpretations of rock bodies. 
(c) The great expense involved in chemical analyses is like- 
ly to limit petrography to members of official organizations and 
men of means or leisure. The average petrographical worker 
of today among teachers can not command numerous high- 
class silicate analyses. (The use of slides removes in great 
measure this criticism.) 
5. The five-fold division vitiates the underlying principle 
of the classification in that the rock may be classified on 37.6 
of the contents disregarding 62.4 of the same. This difficulty 
is moist manifest in the Salfemanes although the rocks known 
introduce few major difficulties. 
III. Conclusion. 
The new classification will not in itself supplant the present 
nomenclature, but will furnish a means of expressing concisely 
the chemical position of a given rock in much the same way 
as the scientific nomenclature of botany is related in the pres- 
ent popular terms. 
