PETROGRAPHY. 143 
positions and partly by their textural characters. The same is the case to a still greater 
extent with the leucite-tephrites, which are here referred to at least eleven types, while 
the leucite-trachytes have been split up into six types, and the leucitites into seven. 
In part this is due to a recognition here of differences, either modal or textural, 
which have been usually disregarded either because they have been thought to be 
of minor importance or through a certain reluctance to add to the terminology of 
petrography. In part also it is due to the fact that a very considerable portion 
of the rocks under investigation are so extremely scarce and so rarely met with out- 
side of the Roman Region that any recognition of differences between them has been 
thought to be "not worth while." In regard to this last it may be said that to be 
logical and consistent throughout petrography should apply its principles of classi- 
fication and nomenclature impartially and irrespective of the commonness or rarity 
of the objects studied. This is one of the fundamental principles of the quantita- 
tive system in regard to the chemical and mineralogical constituents,* and, it may 
be added, in regard to the textural characters as well. 
But, however reluctant one may be to increase the "burden of new names," 
and therefore endeavor to force clearly distinct types into old frames, as by 
calling missourite a leucite-gabbro; and however neglectful petrographers may be 
of the less well-known rocks, and therefore content to lump together the obviously 
unlike, there is a growing recognition of the need of increasingly finer distinctions, 
which is felt even with the rarest types as the petrographical knowledge of the 
remote portions of the earth increases. 
This need is met, not only by the frank use of new names, but in part by ref 
erence of rocks belonging to the larger groups to certain "types," and in part by the 
use of qualifying adjectives. As illustrations of these, and as correlating the two 
systems, it may be pointed out that the ischial phlegrose corresponds fairly well with 
Rosenbusch's "Ponza typus" of the true trachytes, while the cumal phlegrose is 
approximately the same as his "phonolitic trachyte," though there are textural dis- 
tinctions made in the quantitative system which do not obtain in the prevailing 
ones. Similarly, the tavolatal appianose is distinguished from the other leucite. 
tephrites as of the "phonolithoid type." Again, the types of galeral and hernical 
braccianose, that is, leucitites which carry a little labradorite, are distinguished from 
the romal or saccal albanose (feldspar-free leucitites) by the adjective "tephritic." 
It would lead us too far astray to discuss further this important topic, but the 
general facts thus briefly pointed out will serve to indicate the lines along which a 
correlation of the types of the two systems may be studied. 
* Cross, Iddings, Pirsson, and Washington, op. tit., p. 108. 
