GENETIC CLASSIFICATION OF PHENOMENA S15 
may be mentioned, for examples, weathering, erosion, deforma- 
tion, transportation, and deposition. These are names that, as 
technical terms, do not now mean very much. While they are 
commonly used, and perform useful functions in certain cases, 
they really indicate an imperfect state of knowledge of the sub- 
ject, or rather remissness in careful discrimination. All are 
compound processes, and involve the simultaneous action of 
several distinct agencies. Weathering includes, among other 
changes, the mechanical breaking down of rock-masses through 
the effects of heat and cold, the action of life or the application 
of pressure (disintegration); it involves the chemical alteration 
of some of the essential constituents, by which the identity of 
the rock-mass is lost (decomposition) ; and it also embraces, 
in its earlier stages, chemical change in which traces of the 
identity of the original rock are retained, but in which there has 
been some metasomatic replacement. 
In the same way most of the other terms applied to “pro- 
cesses” are found to be ill-defined. Even metamorphism, which 
is, in the present connection, used in its limited petrographic 
sense, is a loose title. Usually it carries with it the idea of rock 
induration. Its complexity is hinted at by the use of such com- 
pounds as ‘‘contact”” metamorphism and ‘‘regional”’ metamor- 
phism. It actually embraces both metasomatic and paramorphic 
alteration, and sometimes also mineralization and cementation. 
Certain diastatic and vulcanic influences also profoundly affect 
its exact expression. 
To one trained in some other than geological science, the 
most striking feature of the latter is a certain vagueness that 
seems to pervade the entire field. This is also the main difficulty 
that every beginner has to overcome. While after a time this 
trouble ceases to impress itself on the geologist himself it is 
nevertheless glaringly apparent in his conversation and especially 
in his writings. The outcome of closer attention to the only 
natural scheme of classification, the genetic one, is clearer dis- 
crimination of facts, greater precision of statement, and vastly 
better comprehension of the whole subject. 
CHARLES R. KEYES. 
