DEAINAGE OF FOEEST-SOIL. 237 



verj generally recognized, both as a theoretical inference and as 

 a fact of observation ; but the eminent engineer Belgrand and his 

 commentator Yalles have deduced an opposite result from various 

 facts of experience and from scientific considerations. They con- 

 tend that the superficial drainage is more regular from cleared 

 than from wooded ground, and that clearing diminishes rather 

 than augments the intensity of inundations.* l^either of these 

 conclusions appear to be warranted by their data or their reason- 

 ing, and they rest partly upon facts, which, truly interpreted, are 

 not inconsistent with the received opinions on these subjects, 

 partly upon assumptions which are contradicted 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 np the fissures 

 in the rocks, so as to impede the passage of water through chan- 

 nels 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 opera- 

 tions of sylvan nature. Hain-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 remain only 

 tmtil 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 sudden frost suc- 

 ceeds a thaw at the close of the winter, after the snow has prin- 

 cipally disappeared, the water in and between the layers of leaves 

 sometimes freezes into a sohd crust, which allows the flow of 

 water over it. But this occurs only in depressions 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 



* Belgrand's observations are confined to forests of deciduous trees, and, 

 while he maintains the above opinions, he still admits the vast utility of the 

 woods in preventing waste of earth. — La Seine, 1872, p. 405. 



