DRAINAGE. 113 



proportion of the rainfall to drain directly into the 

 river channels than will a surface covered by 

 vegetation. This is especially the case during the 

 colder parts of the year, when the ground is frozen. 



"When rain falls on a surface covered by vegeta- 

 tion, the water, by slowly trickling down the stalks 

 or stems of the leaves and the branches and trunks 

 of the trees, finds a ready entrance into the ground 

 by following their surfaces and discharging into 

 the porous ground lying around their roots. 



A forest permits this action of the water in sink- 

 ing into the ground to take place quite readily. 



A forest, therefore, tends to decrease the amount 

 of rainfall that drains directly from the earth's 

 surface. 



A forest also tends to prevent the occurrence of 

 too little water in a river, because it insures the 

 filling of the reservoirs of springs, which discharge 

 their waters into the rivers during the intervals 

 between the rainfalls. 



Unless, therefore, forests are preserved, the 

 proper drainage of the earth will be disturbed, 

 and the rivers will have too much water in their 

 channels during the time of rains, and too little 

 water in the intervals between rains. 



The rapid drainage of the surface when no 

 h 10* 



