194 
ABE SOILS ENRICHED, IMPOVERISHED, [Part III. 
being richer in soil than the tops or sides of the 
hills, owing to the gentle gradients of the bot¬ 
toms of the valleys; for, other things the same, 
that is, in the same strata, with the same vege¬ 
tation, &c., one universal result of the wash of 
rain is, that the degree of denudation of soil will 
be directly as steepness. 
Some of these dry valleys have an almost im¬ 
perceptible slope; and they might be perfectly 
level, and yet be regular channels for the wash 
of periodical heavy rains. For if water can get 
out at one end of a level channel, and cannot get 
out at the other end or at the sides, it not only 
will, but must , get out where it can — 
“ Unda impellitur unda 
Urgueturque prior venienti, urguetque priorem;” 
and it will carry with it much of the finer soil 
formed by disintegration and vegetation. 
When these chalky downs are ploughed up, 
the brow of the hill shows light, and the soil 
darkens in descending. If this is not from the 
wash of rain, what is it from ? If it is, the wash 
of rain must be considered as a very universal 
agent. 
The lateral wash of rain acts constantly to fill 
valleys. The longitudinal scooping force of rain 
and the run of rivers constantly counteract this. 
