Editorial Comment. 49 
were proposed or various modifications suggested of existing 
schemes, each of which served to illustrate the condition of 
knowledge at the time or, perhaps, merely the writer's con- 
ception of that knowledge. Naturally, all failed, though this 
not necessarily through fault of those making the attempt, but 
rather through the fundamental fact that sufficient information 
was not available — the time had not arrived. 
The principal result of the attempts of the past twenty 
years, as manifested in the literature, consists in the coining of 
new names, the criteria for which were furnished bv each 
worker independently. It is perhaps still a question if we 
have arrived at a sufficient knowledge of the essential criteria 
for a satisfactory classification. Be this as it may, attempts are 
still being made and the one now before us is sufficientlv ser- 
ious to demand more than a passing notice. 
And first, it should be stated that, whatever may be one's 
personal views on the subject, he can but be impressed with 
the fact that the Quantitative Classification of Igneous Rocks, 
as recently issued by the University Press of Chicago, is the 
work of good authorities. Had American petrologists been 
called upon to name four individuals who, by training and 
profession, were best qualified to undertake this task, it is safe 
to assume that a very large majority of them would have de- 
cided without hesitation upon the four whose names are given 
on the title page. 
The work begins with chapters on the views held prior to 
the nineteenth century and on the development of systems dur- 
ing the nineteenth century, this being followed by a chapter 
on the beginning and development of the microscopical era. 
These chapters constitute about one-third of the book and 
form a very satisfactory historical resume. 
The part relating to the classification now put forward is, 
however, of primary interest. As here treated, all igneous 
rocks are classified on a basis of their chemical composition, 
all rocks having like composition being grouped together. The 
definition of the chemical composition of a rock is expres 
in terms of certain minerals such as are capable of crystallizing 
from the magma of a given chemical composition, the expres- 
sion being quantitative. < Itherwise expressed, the classifica- 
tion is primarily magmatic. These arc fundamental principles 
