492 W. J. McGee—Dynamical Geology. 
to practically traverse the domain of geologic science, is summarized 
in the accompanying table :— 
Classification of Geologic Processes. 
1. Deformation Elevation 
Principal { Depression 
Categories. | 2. Gradation Degradation 
{ Deposition 
(1. Vulcanism Extravasation 
(ones of do. 
2, Alteration Lithifaction 
{ Converse of do. 
Subordinate } 3. Glaciation Glacial construction 
Categories. 4 { Glacial destruction 
4. Kolation Folic construction 
{ Eolie destruction 
5. Vital action Various constructive and 
{ destructive processes. 
The first principal category of processes is supplemented by the 
first subordinate category, and both tend to produce departures from 
the simple geoidal form or heteromorphism. Play is thus given to 
the operations of the second principal and the last four subordinate 
categories, which are also intimately related, and, combined, tend to 
produce heterogeneity in the external shell of the earth. The joint 
result is differentiation of the earth’s exterior—the converse of those 
processes of concentration and segregation by which the planet was 
originally formed ; and the passage from the stage of segregation to 
that of differentiation represents at the same time the senescence of 
the planet and its entrance into the state recognized by the geologist 
per se. 
Now the processes involved in heteromorphism are generally 
obscure, and many of them are beyond the reach of observation. 
Here, moreover, the domain of the physicist and astronomer on the 
one hand and that of the geologist on the other overlap; here the 
physicist contributes principles and makes deductions of great sug- 
gestiveness and often of high value to the geologist, and here the 
geologist is an agnostic and assails the deductions of the physicist, 
and, too often for the good repute of physical science as applied to 
geologic research, breaks them down; here, too, the geologist is 
equally an agnostic with respect to his own conclusions of higher 
rank than mere generalizations, and assails every inference of his 
fellows and, unless he be rash indeed, guards his own course at 
every step and feels his way cautiously through the tangled maze of 
ambiguous testimony recorded in the crumpled strata of the moun- 
tains; here the dearth of clear definitions of the various processes 
of deformation is doubtless due to the hesitation of physicist and 
geologist alike to confidently enter the purview of the adjacent 
domain; but here tentative definitions (at least) are especially 
needed, and indeed essential to the progress of research. 
Within about a decade an inference of moment concerning diastatic 
movement has been made (largely by American geologists), viz. 
that certain orogenic and even volcanic movements are consequent 
