1879. | Geology and Paleontology. 531 
THE CLASSIFICATION OF Rocks.—Mr. M. E. Wadsworth pub- 
lishes in the Bulletin of the Museum of Comparative Zodlogy of 
ambridge! an abstract of a thesis on the classification of rocks, 
from which we extract the following: “No natural distinction 
can be drawn between rocks of the Tertiary and Pre-Tertiary ages, 
since the glass and fluidal inclusions, ia ait texture, and the 
various other characters fail, exactly where they are most needed, 
to divide the rocks into older and nosis as is done by the 
majority of lithologists, 
“The writer believes that rocks should be studied, by begin- 
ning with their most compact or glassy state, and by then tracing 
them through to the most orystallige form, following every altera- 
tion, whether it be chemical or mechanical. Every | rock that can 
be traced in this way forms a distinct species, whatever may be 
its state,—whether amorphous, glassy, crystalline, fragmental, 
tufaceous, or otherwise,—and whatever may be its age. The 
modifications, if of sufficient importance, form varieties simply, 
which should be included under the specific name. A natural 
classification of rocks must be empirical, and must be based on 
the rock as a whole, while a natural mineralogical classification is 
an impossibility, as it is based on part of the ‘characters on 
“If we except the veinstones and the majority of those keks 
that are composed of one mineral, the species of rock forming the 
crust of the globe are very few. Believing that this earth is a 
cooling globe, all manifestations of internal heat giving rise to 
forms came primarily from volcanic ones, volcanic energy having 
been more active than now in the past ages of the globe. This 
derivation is consonant with that which we see taking place at 
the present time, and agrees with the law of dissipation of energy; 
while the reverse view, at present popular,—that eruptive rocks 
were derived from sedimentary ones,—is contrary to the positive 
testimony of the rocks themselves, to the facts that are observed 
in nature, and to physical laws. 
“ Taking the aerate of any rock as its initial point, the 
minerals and rock fi ents contained therein fall naturally 
sp three classes : 1. Miben and fragments of prior origin ; 
he Poh se tiat consolidation ; 3. The products of altera- 
tion and infiltrat 
“These three prie are most marked in the volcanic rocks, as 
is natural; the first two predominating in the younger and least 
altered, the latter in the older and more altered ones, while the 
first and third classes predominate in sedimentary rocks, These 
alterations apparently take place through the agency of the ordi- 
1 Vol. V., No. 13, 1879. 
