196 GEISTEEAL EESULTS. 



sliaE find that probably not one-tenth of the total superfides of 

 our planet was ever, at any one time in the present geological 

 period, covered with forests. Besides this, the distribution of 

 forest land, of desert, and of water, is such as to reduce the pos- 

 sible influence of the woods to a low expression; for the forests 

 are, in large proportion, situated in cold or temperate climates, 

 where the action of the sun is comparatively feeble both in elevat- 

 ing temperature and in promoting evaporation ; while, in the torrid 

 zone, the desert and the sea — ^the latter of which always presents 

 an evaporable surface — enormously preponderate. It is, upon the 

 whole, not probable that so small an extent of forest, so situated, 

 could produce a sensible influence on the general climate of the 

 globe, though it might appreciably afiect the local action of aU 

 chmatic elements. The total annual amount of solar heat ab- 

 sorbed and radiated by the earth, and the sum of terrestrial evapo- 

 ration and atmospheric precipitation, must be supposed constant ; 

 but the distribution of heat and of humidity is exposed to dis- 

 turbance in both time and place by a multitude of local causes, 

 among which the presence or absence of the forest is doubtless 

 one. 



So far as we are able to sum up the results, it would appear 

 that, in countries in the temperate zone still chiefly covered with 

 wood, the summers would be cooler, moister, shorter, the winters 

 milder, drier, longer, than in the same regions after the removal 

 of the forest, and that the condensation and precipitation of at- 

 mospheric moisture would be, if not greater in total quantity, 

 more frequent and less violent in discharge. The slender historical 

 evidence we possess seems to point to the same conclusion, though 

 there is some conflict of testimony and of opinion on this point. 



Among the many causes which, as we have seen, tend to influ- 

 ence the general result, the mechanical action of the forest, if not 

 more important, is certainly more obvious and direct than the im- 

 mediate effects of its organic processes. The felling of the woods in- 

 volves the sacrifice of a valuable protection against the violence of 

 chilling winds, and at the same time, the loss of the shelter afforded 

 to the ground by the thick coating of leaves which the forest sheds 

 upon it and by the snow which the woods prevent from blowing 

 away, or from melting in the brief thaws of winter. I have already 

 remarked that bare ground freezes much deeper than that which is 



