949, DRAINAGE OF FOREST-SOIL. 
and his commentator Valles have deduced an opposite result 
from various facts of experience and from scientific consider- 
ations. They contend that the superficial drainage is more reg- 
ular from cleared than from wooded ground, and that clearing 
diminishes rather than augments the intensity of inundations. 
Neither of these conclusions appears to be warranted by their 
data or their reasoning, and they rest partly upon facts, which, 
truly interpreted, are not inconsistent with the received opinions 
on these subjects, partly upon assumptions which are contra- 
dicted by experience. Two of these latter are, first, that the fallen 
leaves in the forest constitute an impermeable covering of the 
soil over, not through, which the water of rains and of melting 
snows flows off, and secondly, that the roots of trees penetrate 
and choke up the fissures in the rocks, so as to impede the pas- 
sage of water through channels which nature has provided for 
its descent to lower strata. 
As to the first of these, we may appeal to familiar facts within 
the personal knowledge of every man acquainted with the 
operations of sylvan nature. Rain-water never, except in very 
trifling quantities, flows over the leaves in the woods in summer 
or autumn. Water runs over them only in the spring, in the 
rare cases when they have been pressed down smoothly and 
compactly by the weight of the snow—a state in which they re- 
main only until they are dry, when shrinkage and the action of 
the wind soon roughen the surface so as effectually to stop, by 
absorption, all flow of water. I have observed that when a sud- 
den frost succeeds a thaw at the close of the winter, after the 
snow has principally disappeared, the water in and between 
the layers of leaves sometimes freezes into a solid crust, which 
allows the flow of water over it. But this occurs only in de- 
pressions and on a very small scale ; and the ice thus formed is 
so soon dissolved that no sensible effect is produced on the 
escape of water from the general surface. 
As to the influence of roots upon drainage, we have seen that 
there is no doubt that they, independently of their action as ab- 
sorbents, mechanically promote it. Not only does the water of 
