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University of California. 



[Vol. 2. 



and the rate of cutting at these points will be approximately the 

 same. If, then, as the writer believes, the altitude of a ridge 

 depends for one of its chief factors on the altitude and rate of cut- 

 ting in the adjacent stream bed ; and if the altitude and rate of cut- 

 ting in neighboring streams of the same class are approximately the 

 same (as just stated), then the adjacent divides should approximate 

 equal altitudes, other things being equal, and an evenness of sky- 

 line in this region will result. These principles should apply to all 

 parts of a drainage system alike, though for the purposes of the 

 present discussion they will be referred to chiefly in connection 

 with the main streams, as it is the uniformity of the main divides 

 which gives a general effect of evenness of sky-line to the region. 



In discussing the question of beveling, the " subequality of 

 mountain heights" will be considered first, without taking into 

 account the lack of horizontality ("tilting") which is associated 

 with it. (This latter point will be taken up later.) Admitting the 

 rough equality at the tree limit, let us consider the question of 

 equality below that point, or the equality in those regions which 

 may never have been above the tree line, bearing in mind that 

 throughout the following discussion of drainage features, mature 

 topograpliy is always postulated. 



Graded Slopes. — In a mature region the streams are in a graded 

 condition. A graded stream is one whose "carrying power is 

 reduced to" essential "equality with the load," and which is thus 

 essentially in a "condition of balance between degrading and 

 aggrading."* Along a stream course, unaffected by accidents 

 from youth to old age, there should never be an absolute balance 

 between degrading and aggrading. The stream taken as a zuhole 

 is cutting all the time, until base-level is reached; but it cuts more 

 slowly as its age increases. The rate of cutting is dependent on 

 the length of the stream course and the elevation of its head-waters 

 above its mouth (or the grade of the stream); and also on the 

 amount of precipitation, general character of the rocks in which it 

 cuts, and amount of material brought into the stream from the 



*Wm. M. Davis: Physical Geography in the University; Journ. Geol., 

 Vol. II., No. 1, Jan.-Feb., 1894, p-77. 



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