DISTRIBUTION OF THE EAINPALIi. 293 



Sect. IV. — On the Local Effects of Forests on the Distribution of the 

 Rainfall within the Forest District. 



While the primary distribution of forests appears to have been 

 determined by the general distribution of the rainfall, forests appear 

 to influence the subordinate distribution of the rainfall, both in time 

 and space, over the forest district ; and irrespective of this, though 

 connected therewith, they exercise an important influence on the 

 disposal or distribution of the rainfall within the district in which 

 they exist. 



The most manifest of the effects of forests on thq rainfall is that 

 which they exercise upon the distribution of it after it has fallen. 

 Of the water which falls as rain a portion is evaporated, a portion is 

 absorbed by the ground, and a portion immediately flows back again 

 toward the sea ; each of these is the complement of the others, and 

 their proportions vary under varying conditions; previous to the 

 growth of forests the rush was impetuous ; subsequent to the growth 

 of forests it is restrained. What was then allowed to run to waste, 

 like the extravagant expenditure of the prodigal, is now husbanded, 

 as is the income of the typical pater-familias. 



Cezanne, speaking of the whole series of phenomena brought under 

 review by him in treating of this effect of forests in connection with 

 geological changes, says in a passage I have cited in a volume on 

 " Eeboisement in France " : — 



" There may be given in a few words a resume of the whole series 

 of these phenomena. ' 



" The mountains are the result of a series of upheavals following 

 one upon another in the same region. A. final agitation gave to the 

 different chains of these the existing elevation ; it elevated the 

 summit and opened up deep fissures or divisions, which have become 

 the valleys of the present time. From the time this occurred the 

 waters began to fashion the thalwegs, following the line which best 

 suited them ; wearing down outlets and filling up basins. It is 

 necessary to admit, or to assume, that the depth or thickness of 

 the alluvial deposits in the bottom of certain valleys — for instance, 

 those of the Isfere in the Graisivaudan, or of the Rhine in Alsace, — is 

 to be reckoned by hundreds, and perhaps by thousands, of metres or 

 yards ; for even yet certain lakes existing in depressions of the Alps 

 have their bottom below the level of the sea. 



" After a long series of ages the mountains assumed the leading 



