CONVEXITY OF HILLTOPS 347 
cave. Other factors may be mentioned, but it is probable that they 
acquire prominence only in special cases. 
One of the mentionable factors is wind, which is no respecter of 
slopes, working as readily uphill as down. Another is rain beat. 
The two have this in common: that for each locality they have a 
dominant direction, so that any direct influence they may have on 
topographic expression tends toward asymmetry. 
Fic. 3.—Miniature hills, illustrating the convexity of divides. 
There is an indirect effect of rain beat due to its combination with 
water flow and this follows the direction of water flow. When rain- 
drops beat heavily on the upper slopes there is usually also a diffused 
flow of water. Particles disturbed by the drops are momentarily sus- 
pended by the flowing water and drifted down the slope. Near the 
summit such transportation is favored by the shallowness of the water 
sheet but restricted by the slowness of the current. Lower down it is 
favored by more rapid current but restricted by depth of water, which 
lessens the effect of impact. Whether the ordinary result is greater 
transportation near the divides, tending to produce a convex profile, 
