408 W. M. Davis—Distribution of Drumlins. 
A more complex group could include regions of disordered 
structure, characteristic of mountain ranges, but of very diffi- 
cult subdivision. Here again it is of much importance to recog: 
nize the stage of destructive development, in order to mark the 
contrast between the new, still high and lake-bearing ranges 
ashes and lavas; eolian drifts, like sand dunes; and glacial 
drifts, such as moraines, drumlins and kames, which bring us 
to the special geographic form to be considered here. 
It will be perceived that this grouping does not provide a 
definite place for topographic features of complicated history ; 
it would be difficult, for example, to assign a place for the 
curved trap-ridges in our Triassic formations. This difficulty 
is inherent, for in the blending of inorganic forms we are not 
limited to crossing only between closely related forms as in the 
organic world; crossing, or double control of form occurs here 
even between the first structural divisions. Such blending 
will greatly complicate the resulting forms, and consequently 
evolution by erosion need not yet be discussed. Their name 
should be regarded rather as generic than as specific, for it will 
be shown that hills of somewhat varied form may be fairly in- 
eluded under this term. . 
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