74 ECONOMICS OF FORESTRY. 



drainage long enough to prevent a resultant flood 

 in the river. 



Particular interest in this connection attaches to 

 the influence of forest cover on the melting of snow 

 masses, which gives rise to spring floods. In the 

 dense forest, the snow is usually less deep, a part 

 being intercepted by the crowns of trees and evap- 

 orated, and lies more uniformly, owing to the absence 

 of drifting winds. It is a well-noted experience 

 that it will lie in the shade of the woods from one 

 to two weeks longer, i.e. melt so much more slowly. 

 These elements of distribution in space and time 

 must have an influence upon the rapidity of sur- 

 face flow, and if the soil is not frozen, time is 

 given for percolation and gradual removal. 



Here, again, weather conditions may be unfavor- 

 able, the soil remaining frozen and the melting 

 proceeding rapidly, when the forest effect may be 

 lost. Nevertheless, while the forest effect may 

 become powerless in exceptional cases and under 

 special conditions, the tendency of changing sur- 

 face drainage into subterranean drainage must be 

 beneficial in the majority of cases. It may also 

 happen that the soil conditions, by their loose 

 structure, as in cinder cones, lava, or loose sand 

 hills, are such as to permit percolation readily, 

 when the office of the forest cover can be dispensed 

 with. 



The value of the change of surface drainage 

 into subterraneous drainage becomes apparent in 



