74 THE JOURNAL OF GEOLOGY. 



streams ; these unite, forming constructional drainage systems. 

 If the trough lines are systematically arranged, as among the 

 corrugations of mountain folds, the initial drainage system is 

 definitely located ; if the trough lines are faintly marked and 

 lead irregularly about, as on the nearly level surface of a plateau, 

 the drainage is essentially vague and unsystematic. If the gen- 

 eral descent of the trough lines is here and there reversed into 

 ascent, lakes are accumulated in the basins thus determined ; 

 and this is very common. If the descent of the trough lines is 

 locally intensified, constructional falls or rapids are developed, 

 but this is relatively rare. 



Co7iseqiient drainage. — The constructional streams run down 

 their troughs, carrying along the waste that is washed into them, 

 and trenching channels beneath the initial constructional surface ; 

 or filling constructional hollows ; that is, degrading or aggrad- 

 ing their course, as the necessities demand. As soon as they 

 thus depart from their initial constructional arrangement, they 

 may be called consequent streams. It is true that the construc- 

 tional phase of a drainage system endures only a moment ; 

 yet it seems advisable to recognize this phase by employing 

 a special name for it, before introducing the term, conse- 

 quent, which indicates the much longer phase that next fol- 

 lows. At least, I am for the present experimenting on these 

 two terms with my classes, and find them of value. As long as 

 a stream flows on a line that is essentially the perpetuation of 

 its original constructional course, it may be called a consequent 

 stream ; the trench that it cuts and the valley that is formed 

 by the widening of the trench may be included under the name, 

 consequent valley. Constructional features are encroached upon 

 as the consequent features make their appearance. A con- 

 structional lake decreases in size by filling at the inlet and 

 cutting down at the outlet ; while thus dwindling away, it is a 

 consequent lake. A fall or cascade recedes from its initial 

 constructional position ; but as long as it endures it is a conse- 

 quent fall. 



Subseqtioit drai?iage features. — -As the consequent streams 



