84 OUTLINES OF FORESTRY. 



of it fertilizes the lowlands, over which it is spread 

 during inundations, yet much collects in sand-bars 

 and mud-flats on the lower courses of the river. 

 These flats work injury because : 



1. They hinder navigation, and thus interfere 

 with the commerce between different parts of the 

 country. 



2. They become sources of contamination to the 

 air of the lowlands, by breeding miasmatic and 

 other diseases. 



Besides the disturbances thus caused to the 

 drainage of the region from which the forest has 

 been removed, considerable changes are brought 

 about in the rate at which the now bare soil re- 

 ceives the heat from the sun, and the rapidity with 

 which it throws it off into the air. 



Areas covered with forests both receive and part 

 with their heat slowly, and are, therefore, not very 

 apt to become very hot in summer, or very cold 

 in winter. 



Bare areas, or areas stripped of their vegetable 

 covering, both receive and part with their heat 

 rapidly, and are, therefore, apt to become very hot 

 in summer and very cold in winter. 



The presence of the forest, therefore, tends to 

 prevent marked changes in the temperature of the 



