THE NAMING OF ROCKS 687 
not been possible to drop the new name and place the thing refer- 
red to under a larger division, as one may drop the specific name 
of a new fossil and speak only of the genus to which it belongs. 
Furthermore, the new names of petrography are in most cases 
unlike most of those in biology or in mineralogy, in that the 
things described and given names have no clearly distinguish- 
able characteristics by which they may be recognized. Asa 
result of this inherent vagueness, it is very difficult indeed, from 
the descriptions published, to obtain a clear conception of what 
is meant by many of the new petrographical names. Indeed, it 
may be doubted whether many professional petrographers, to 
say nothing of those who work in other lines of geology, havea 
definite conception of the meaning of many of the fifty or more 
names which have been proposed since 1890. 
Principle underlying naming of rocks.—In giving numerous 
new names to rocks, while no principle is announced by the 
petrographers, the underlying assumption is the same as that 
which prevailed in the early days of petrography; that is, rocks 
may be divided into definite types, which are comparable to defi- 
nite mineral or animal species. I do not for a moment suppose 
that petrographers who have introduced these new names would 
state that they believe this principle. I merely assert that many 
of the numerous names are justified only if the principle be true. 
Responsibility of introducing new names.—The petrographer 
who introduces a new name for a rock assumes a responsibility 
which ought to be incurred only after the most careful consider- 
ation. Probably some of the new names which have been 
recently introduced were necessary to the progress of the sci- 
ence. That many of them were not, I venture to believe. One 
who introduces a new name without the best of reasons for so 
doing is hindering the advance of the science of petrography, 
as well as occasioning loss of time and great inconvenience to 
his fellow workers. 
Statement of the problem.—All\ philosophical petrographers now 
understand that between all kinds of rocks there are gradations — 
from basic to acid, from coarsely granitic to glassy, from rich sodium 
