University of California. 



[Vol. 2. 



unequal bases (CG and AG), the horizontal distance (AG) of the 

 steeper slope will be less than that of the other slope (CG). If the 

 slopes CF and CE have CG in common, and the grade of the 

 first is greater than that of the second, then the altitude of the first 

 (FG) must be greater than that of the second (EG). 



From this it follows that in regions of rocks of varying degrees 

 of resistance, either the main stream channels will lie nearer (hor- 

 izontally) to the summits of the harder rocks, the summits remaining 

 at a uniform altitude, or else, the horizontal distance' of the summit 

 from the stream being the same, slopes are developed by a dif- 

 ferential lowering of the summits. The adjustment by either of 

 these methods is usually modified through the development of the 

 minor drainage lines. The tendency is always, of course, to attain 

 the desired end by the simplest means. 



Similarly, along the minor streams, graded slopes may be 

 attained in one or both of the following ways. If the spaces 

 between streams of the same class are the same in both hard and 

 soft rocks, then to attain graded slopes the stream canons in the 

 harder rocks must be relatively deeper than in the softer rocks; or, 

 in other words, the minor ridges must be at a greater elevation 

 above their stream beds. If the depth of the cutting is relatively 

 no greater in the hard than in the soft rocks, then graded slopes 

 may be attained only by having the streams more numerous in the 

 hard than in the soft rocks — that is, horizontally nearer their divides 

 (as explained above for the main streams) and therefore closer 

 together. Further, on account of the steeper grades in the harder 

 rock, the branch stream courses will be shorter, in general, than 

 those in the softer rock, with equal vertical range in the two cases. 



From the above it follows that in the less resistant rocks the 

 slopes will be less dissected than in the more resistant. The slopes 

 will also be gentler, the summits and the intervening valleys broader, 

 and the latter frequently shallower, in the areas of softer rocks as 

 compared with those of harder. These more rounded and open 

 forms will be contrasted with the more sharply incised forms and 

 steeper slopes found in the areas of more resistant rocks. On 

 account of gentler slopes, as well as on account of less resistance 

 to weathering, the soil will be heavier in the areas of softer rocks, 

 and, generally speaking, a more abundant vegetation will be found 



