NOTES. 445 



by the trees in the process of growth, yet the influence of the 

 soil cover in retarding evaporation is liable to offset this loss, 

 as the soil cover is not itself dried out. 



The forest, then, even if under unfavorable topographical 

 and soil conditions (steep slopes and impermeable soils) it 

 may not permit larger quantities of water to drain off under- 

 ground and in springs, can yet influence their constancy and 

 equable flow by preventing loss from evaporation. 



(3) The surface drainage is retarded by the uneven forest 

 floor more than by any other kind of soil cover. Small pre- 

 cipitations are apt to be prevented from running off superficially 

 through absorption by the forest floor. In case of heavy rain- 

 falls this mechanical retardation in connection with greater 

 subterranean drainage may reduce the danger from freshets by 

 preventing the rapid collection into runs. Yet in regions with 

 steep declivities and impermeable soil such rains may be shed 

 superficially and produce freshets in spite of the forest floor, 

 and an effect upon water conditions can exist only fi-om the 

 following consideration. 



(4) The well-kept forest floor, better than even the close 

 sod of a meadow, prevents erosion and abrasion of the 

 soil and the washing of soil and detritus into brooks and 

 rivers. 



This erosion is especially detrimental to agricultural inter- 

 ests as well as waterflow in regions with thin surface and im- 

 penetrable subsoils, and where rains are apt to be explosive 

 in their occurrence, as in our western and southern country. 

 The best soil of the farms is often washed into the rivers, and 

 the water stages of the latter, by the accumulations of this soil, 

 are influenced unfavorably. 



(5) Water stages in rivers and streams which move outside 

 the mountain valleys are dependent upon such a complication 

 of climatic, topographic, geological, and geographical condi- 

 tions at the head waters of their affluents that they withdraw 

 themselves from a direct correlation to surface conditions 

 alone. Yet it stands to reason that the conditions at the head 



