CONVEXITY OF HILLTOPS 349 
Nevada City, California. The washing away of the auriferous gravels 
laid bare tracts of decomposed granite in which the feldspars are largely 
changed to kaolin, and for about twenty years these have been 
exposed to the elements. There can be little question that here the 
convexities are due to creep; and the miniature topography illustrates 
strikingly the contrast between creep and stream work; but the con- 
ditions are not so near to normal as to make the forms fully repre- 
a 
Fic. 5.—Erosion and sculpture by the beating of raindrops. The material is 
regolith, exposed in a road cutting. The rain was driven by a strong wind so as to 
strike the ground in an obliquely ascending direction, from right to left. 
sentative. The kaolin is so cohesive when wet as to tolerate slopes 
far above the ‘“‘angle of repose,” and this leads to an exaggerated 
expression of the convex profile, shown especially in Fig. 2; and in 
the other examples there is reason to believe that the positions of 
gullies were largely determined by shrinkage cracks. 
Fig. 5 illustrates the power of raindrop impact to attack unpro- 
tected surfaces of waste. In ordinary examples of rain sculpture the 
