134 



PRINCIPLES OF STRATIGRAPHY 



of other streams Extended consequents, by reason of their greater 

 water supply, are apt to become compound or at least their principal 

 branches will be affected in this manner. This is especially the case 

 with the subsequent type of stream. The present Moselle of 

 western Europe is an example of a compound river, having ac- 

 quired by capture some of the headwaters of the Meuse. (Davis, 

 io:22p-2^o.) (Figs. 22, 23.) 



A composite stream is defined by Davis as one including in its 

 basin, drainage areas of different structure. In so far as the differ- 



Hypothetical sketch map of the 



Aleuse and Moselle rivers, 



France, before capture. (After 

 Davis.) 



Fig. 2^. Map of the Meuse and the Mo- 

 selle after capture. (Davis.) 



ence in structure affects the stream, causing it to modify its course, 

 this definition may stand. We must, however, bear in mind that we 

 are dealing with two distinct things, the river and the drainage 

 basin. A simple consequent on a destructional surface (peneplain) 

 or a superimposed consequent on a much folded older terrane may 

 flow across regions of different structure in different parts, i. e., 

 have a composite drainage basin and yet be of simple character. 



The third type of polygene river is the complex. This is defined 

 by Davis as a river which "has entered a second or later cycle of 

 development." Rivers inherited by an uplifted peneplain from the 

 previous cycle are typical examples of this class. They will differ 

 from simple consequents upon a peneplain in that they have ac- 



