INFLUENCE OF FORESTS ON CLIMATE. 15 



taken into consideration when making observations in 

 regard to the influences of forests on climate. There may 

 be long series of years in which drouths will prevail, 

 even in close proximity to very extensive forests, and 

 these may be succeeded by seasons in which an unusual 

 amount of rain will fall, but these extremes occur in all 

 countries, and they do not prove that the average amount 

 of moisture during a longer series of years has been in- 

 creased or diminished by physical changes of the earth's 

 surface, wrought by the direct agency of man. It must 

 not be supposed that a few acres, more or less of forests, 

 will produce any appreciable effect on the climate of the 

 surrounding country, but they may, and in fact, usually 

 do have a local influence in preserving humidity as well 

 as affording shelter and protection against prevailing 

 winds. 



FORESTS AND STREAMS. 



In all forests there is more or less vegetable matter, 

 made up of leaves, twigs, old wood, mosses, and decaying 

 herbaceous plants, all of which go to make up a sponge- 

 like mass, covering the earth and filling the interstices 

 between rocks, or perhaps such has been washed into 

 depressions where the land is uneven or much broken up. 

 But in whatever position it rests it absorbs and retains a 

 large amount of water that falls in rains, or is produced 

 from melting snow, until it slowly sinks into the soil 

 below or is dispersed by evaporation. A part of that 

 which passes into the soil is taken up by the trees, and 

 exhaled by their leaves, thereby adding humidity to the 

 surrounding atmosphere ; another part passes beyond the 

 reach of the roots, and finding subterranean channels is 

 carried onward until it again comes to the surface in 

 springs, or sinks to some lower depth and entirely dis- 

 appears. 



That the vast deposits of vegetable matter in our great 



