1889 .] 
367 
[Davis and Wood. 
as presented in the “Geology of the Head of Chesapeake Bay” in 
the Seventh Annual Report of the U. S. Geological Survey ; and 
of the account of the Topography of New Jersey by C. C. Ver- 
meule lately published in the first volume of the Final Report of the 
State Geologist, Prof. George H. Cook. In the untimely death of 
Professor Cook we have lost the leader under whose direction 
nearly all of the published data on which our work rested was 
prepared. 
Introduction. 
2. General scheme of geographic classification. The surface of the 
land may be regarded as composed of a number of individual forms, 
whose general character depends on the rock-structure which the 
processes of land-sculpture have worked upon, and whose more par- 
ticular expression depends on the degree of advance in the deg- 
radation of the surface from its initial, constructional form to the 
smooth, low, baselevel plain to which it is finally reduced. Thus 
regarded, any geographic individual may be associated with cer- 
tain others, to which it is related by similarity of structure, and 
the whole group of similar individuals, thus related, may be ideal- 
ized in a t}’pe, which presents all the essential, but none of the 
accidental features of the group that it represents. The type is there- 
fore an elastic conception, not limited in the way of size, nor in 
the number of its features, nor in any variable element ; but 
always holding fast to those characteristics that distinguish it 
from the types of other groups. Moreover, in order that in- 
dividuals of different age may be properly represented by a sin- 
gle type, every type must be conceived to vary systematically 
in passing through the cycle of changes that its individuals suf- 
fer from the time when the first attack is made upon them by the 
destructive forces of the weather, to the time when they are worn 
down to baselevel, the level of the standing water into which their 
drainage flows, below which land erosion cannot reduce them ; and, 
if they front on the sea, their type will include a coast-line with its 
varying expression from the early time when the waves make their 
first attack upon it to the distant end when the whole is planed down 
to a flat submarine platform at an undetermined depth. Indi- 
viduals under a type may then be regarded in natural relationship ; 
they are not final results of processes, but are stages in a cycle 
of systematic change, and are therefore to be regarded not only 
