1 7) I Tin American Geologist September, 1893 
convenient so ms to be of practical utility. These conditions 
are rarely if ever absolutely fulfilled, for in every branch of 
science there is a more <>r less complete gradation so that 
some features refuse to connect themselves naturally with any 
division, and must be classified arbitrarily. This is especially 
true of geomorphy, which abounds in transitional and prob- 
lematical forms, so that any classification is at best onl}- 
approximate. 
The system that first suggests itself is one based upon ex- 
ternal form. For ordinary purposes it is of practical utility. 
but from its superficial character is of little scientific value, 
for it places together features of widely different origin while 
separating others that are closely related genetically. It is 
impossible, moreover, to make the divisions of such a system 
exact, since it is impossible to draw sharp lines between dif- 
ferent forms which merge into each other through transitional 
forms. There is also lack of a complete and accurate ter- 
minology. The term "mountain" for instance is vague and 
almost impossible accurately to define, for there is no sharp 
line separating a mountain from a plateau, mesa or hill. 
It is desirable, then, to devise some system that avoids the 
consideration of external form as a basis. The least objec- 
tionable plan is a genetic classification. It accords best with 
the spirit of modern science, which is concerned more with 
natural processes than with their products. Any classification 
by genesis has the disadvantage of grouping together dis- 
similar forms, but even the most dissimilar products of any 
given process have some common characteristics that distin- 
guish them from similar products of any other process. Thus 
all features due to glacial action are naturally connected, and 
it is natural to group together all volcanic products even if 
they are as different as a cinder cone and a lava plain. 
All natural agencies tend either to build or to destroy, and 
so all topographic forms may he classed as the result either 
of constructive or destructive action. They may he again 
divided according to the particular agencies which have given 
them their chief characteristic-. 
It is necessary, however, first to place outside our system 
one great agency, that of general deformation, which alone 
has rendered possible the action of all other geological pro- 
