140 L. E. HICKS — SOME ELEMENTS OF LAND SCULPTURE. 



observation, I will add two observations suggested by the above quota- 

 tion. 



In the first place, the remark of Gilbert that "where the Hanking 

 slopes are as steep as represented in the diagram, the convexity on the 

 crest of the ridge has a breadth of only two or three yards, but where 

 the flanking slopes are gentle, its breadth is several times as great,'' 

 conveys a partial truth, and at the same time suggests a broader truth. 

 Gilbert merely affirms a relation between the steepness of the decivities 

 and the breadth of the convex portion of the crest; but both of these 

 correlated elements of form depend upon the relative intensities of water 

 sculpture and weathering, and these in turn depend upon the struc- 

 ture and the stage of base-leveling in the given region. The general 

 law of relative intensities may be stated as follows: If water sculpture 

 predominates, the slopes will be steep and the divides narrow and high ; 

 and, conversely, if weathering predominates, the slopes will be gentle and 

 the divides broad and low; but this general law is profoundly modified 

 by structure and time. The broad, flat blocks which, as we have seen 



ct 



Figure 8. — Illustrating the Co-i cistt nee of steep Slopes with broad weather Curves in an tarty Stage of 



Base-leveling. 

 fi«() = weather curve ; b c = water curve. 



above, are the normal types of raw material to be moulded by land 

 sculpture, yield broad weather curves in the early stages of base-leveling 

 wholly on account of their primitive structure. This is an exception to 

 the general law, inasmuch as water sculpture is usually energetic in these 

 early stages, and yet the weather curves are 1 >r< >ad. 1 1 is als< » an exception 

 to Gilbert's statement that the crest is narrow if the slopes are steep. 

 Many cases occur in the earlier stages of base-leveling in winch broad, flat 

 weather curves are conjoined with very steep water curves, as in figure 8. 

 Many cases also occur in the same early stages of base-leveling in which 

 the crest is narrow and the slopes steep, as affirmed by Gilbert and illus- 

 trated by his figure G'>. For example, the same mesa represented in 

 cross-section by figure 8 would present many subordinate ridges between 

 its lateral ravines with steep slopes and narrow crests. It is evident, 

 therefore, that in this early stage of base-leveling, structure is the domi- 

 nant factor whether the crest is narrow or broad. The steep water 

 curves are the direct result of structure, since it is only by upheaval 



