The Cycle of geograjjJiic Development. 73 



which I may outline, since without them no progress can be 

 made: The first is that every land form passes through a com- 

 paratively systematic series of changes from its youth, when its 

 form is defined chiefly by constructional processes, past its 

 maturity, when the processes of sub-aerial sculpture have carved 

 a great variety of mouldings and channellings, toward its old 

 age, in which the accomplishment of the full measure of denuda- 

 tion reduces the mass essentially to baselevel, however high it 

 may have been originally. I have become accustomed to call 

 this unmeasured time a geographical cycle. It may be long for 

 a structure of hard rocks, or shorter for a structure of weak rocks ; 

 but in both the sequence of immature, mature, and senile forms 

 is essential. The particular expression of these forms varies with 

 the structure of the mass concerned ; but for every structure there 

 is an appropriate sequence of young, mature, and old features. 



It is therefore important to determine in accordance witli this 

 fundamental principle the stage in which any given area stands 

 in its life's journey. The standard descriptions of many of our 

 states gives no such account of their topographic forms, and 

 the student or teacher who seeks it has little reward. The 

 account is needed not only because the reader can gather from 

 it a better understanding of the relations of a region to the rest 

 of the world, but also because such an account enables him to 

 appreciate much more closely and more easily the actual forms 

 of the region itself. 



A second important principle is in a measure a corollary of 

 the first : At any time during a geographical cycle a land area 

 ma}^ be disturbed b}^ depression or elevation. A new relation 

 is then established Avith the baselevel of drainage, and a new 

 cycle of denudation is introduced. The forms developed by 

 denudation in the first incomplete cycle then become, as it were, 

 the constructional forms of the new cycle, and from those as a 

 beginning the forces of denudation go on aiiew. The combina- 

 tion of the topographic features developed in the two cycles 

 produces what I have called " composite topography," and this is 

 of extremely common occurrence — for an example, we may 

 refer again to the dissected plateau of southern New England. 

 The upland with its residual mountains is the product of an 

 earlier cycle ; the valleys are the work of a later cycle ; the 

 glacial features may be referred merely to a short-lived climatic 

 episode late in the second cycle, so brief was the occupation of 



