PHYSICAL GEOGRAPHY IN THE UNIVERSITY. 73 



graphical cycle. Construction, destruction, baselevel and cycle 

 are our primary terms. A full understanding of the destruc- 

 tional processes requires deliberate study of mineralogy and 

 lithology, chemistry and structural geology ; a good understand- 

 ing of constructional forces and processes has not yet been 

 gained, but a review of the advance made towards it carries the 

 student through a wide range of geological theories, in which 

 physics and mathematics are continually appealed to — perhaps 

 sometimes with too great a confidence in the applicability of 

 their conclusions concerning an ideal earth to the case of the 

 actual earth. 



If the cycle of destructive development is not interrupted, 

 any constructional form will ultimately be reduced to a monoto- 

 nous baselevel plain of denudation. This is a broad abstract 

 statement. It is simply the first framework of the geographical 

 scheme. It is a mere sketch in faint outline, needing all manner 

 of finishing before its full meaning can be made out. It must 

 be filled in by the gradual addition of details. The first step 

 involves the recognition of the systematic sequence of topo- 

 graphic forms produced during the accomplishment of the 

 destructive work. This should be considered before classifying 

 the various kinds of constructional forms on which the destruc- 

 tional processes begin their tasks. Whatever constructional form 

 exists at the beginning of the cycle, there is a certain general 

 succession of features common to nearly all cases of geograph- 

 ical development. The understanding of this succession calls 

 for the study of river systems and the general drainage of the 

 land under their guidance ; because it is so largely under the 

 control of these processes that the destructive forces do their 

 work. 



Constructional dramage. — At the beginning of a cycle, there 

 are relatively broad, massive forms, on which the carving of the 

 destructive forces has made no mark. The unconcentrated 

 drainage, or wet-weather wash, takes its way down the steepest 

 slopes of the constructional surface, until the supplies from either 

 side meet obliquely in the trough lines, forming constructional 



