LAND WATERS STREAMS 



127 



process of tributary development goes on until drainage lines of 

 i the fourth, fifth, sixth, and higher orders are formed (Fig. 93) . 

 j Since the process of valley development under such circumstances 

 i is also the process of ridge dissection, a stage is presently reached 



Fig. 93. Diagrammatic representation of a surface much dissected by the 

 development of numerous tributaries. 



where the ridges are cut into such short sections that they cease 

 to be ridges, and becomes hills instead. Even then the processes 

 of erosion do not stop, for rain-water falling on the hills washes 

 the loose material from their surfaces, and starts it on its seaward 



Fig. 94. Diagram showing streams in adjacent valleys, undercutting the 

 divide between them. They may, in time, destroy the divide by lateral 

 planation. 



journey. Thus the "everlasting hills" are lowered, and, given 

 time enough, they will be carried to the sea. 



The base-leveled surface is not absolutely flat. The area 

 reduced by each stream will have a slight slope down-stream, and 

 from its sides toward its axis. The low divides between streams 



