REPORT OF THE DIRECTOR, 1922 105 
THE NEW PETROLOGY 
BY CHARLES P. BERKEY 
I suppose that one is not far wrong in saying that petrology 1s the 
science of rocks; but we have not.made ourselves very clear by say- 
ing it. To the average student of the subject, who must judge from 
what he is taught and from what he can find in texts, petrology looks 
like a very complicated lot of methods of discrimination, coupled 
with still more complicated schemes of classification, by means of 
which one sometimes succeeds in finding a sufficiently mystifying 
name for a very innocent-looking fragment of rock to satisfy a per- 
fectly natural craving for worthwhileness. 
But this is not petrology — the real petrology that ought to be — 
no matter how elaborate it is or however minutely every little detail 
may be described. It is one kind of rock study, one form of petrol- 
ogy. The description of rocks is a form that, no doubt, has served a 
very good purpose in collecting and recording and classifying data; 
but there are other things to be done. 
After the first step in a new scientific field is taken, it is not suffi- 
cient to present simply long lists of names and descriptions and 
descriptive terms and tabulations of facts and classification schemes. 
Such data alone do not satisfy the legitimate demands for an 
explanation of some kind. Such natural grouping of rocks as has 
been attempted is a first step toward meeting this demand, but it has 
not gone far enough in petrology. 
The Field 
It is easy to assume or to adopt too simple a conception of the 
term rock. It is clearly in the interest of beginners for them to 
think of a rock as a mineral aggregate representative of a structural 
unit of considerable magnitude, and as a very definite and constant 
and reliable thing. But this is no great advantage to the investigator ; 
and to insist on its magnitude and constancy may be very misleading 
indeed. 
Petrology by rights includes the whole range of natural products 
of definite mineral makeup — all kinds of mineral aggregates, all 
kinds of origin, and all sorts of conditions. 
In actual investigations it is a mistake to be content with the types 
of material representing only the more apparent large physical units. 
Some insignificant-looking portion, usually too unimportant-looking 
