EFFECTS OF DESTRUCTION OF FORESTS. 107 



supplying their trees with nourishment from a soil deepened and 

 enriched from the decomposition of their foliage, or sending out long 

 rootlets into the surrounding earth in search of juices to feed them.' 



" But with all the provisions which have been made for the produc- 

 tion of forests, and for the restoration of small portions which have 

 been destroyed, it is possible for man to counteract these ; and he 

 has done so. But what have been some of the consequences which 

 have followed ? 



" According to a summary of some of these given by Marsh, ' With 

 the extirpation of the forest all is changed. At one season the earth 

 parts with its warmth by radiation to an open sky ; receives, at 

 another, an immoderate heat from the unobstructed rays of the sun. 

 Hence the climate becomes excessive, and the soil is alternately 

 parched by the fervours of summer, and seared by the rigours of 

 winter. Bleak winds sweep unresisted over its surface, drift away 

 the snow that sheltered it from the frost, and dry up its scanty 

 moisture. The precipitation becomes as irregular as the tempera- 

 ture ; the melting snows and varied rains, no longer absorbed by a 

 loose and bibular vegetable mould, rush over the frozen surface, and 

 pour down the valleys seawards, instead of filling a retentive bed of 

 absorbent earth, and storing up a supply of moisture to feed 

 perennial springs. The soil is bared of its covering of leaves, broken 

 and loosened by the plough, deprived of the fibrous rootlets which 

 held it together, dried and pulverized by sun and wind, and at last 

 exhausted by new combinations. The face of the earth is no longer 

 a sponge, but a dust heap ; and the floods which the waters of the 

 sky poured over it hurry swiftly along its slopes, carrying in suspen- 

 sion vast quantities of earthy particles, which increase the abrading 

 power and mechanical force of the current, and, augmented by the 

 sand and gravel of falling banks, fill the beds of the streams, divert 

 them into new channels, and obstruct their outlets. The rivulets, 

 wanting their former regularity of supply, and deprived of the 

 protecting shade of the woods, are heated, evaporated, and thus 

 reduced in their former currents, — but swollen to raging torrents in 

 autumn and in spring. 



" * From these causes there is a constant degradation of uplands, 

 and a consequent elevation of the beds of water-courses, and of lakes, 

 by the deposition of the mineral and vegetable matter carried down 

 by the waters. The channels of great rivers become unnavigable, 

 their estuaries are choked up, and harbours which once sheltered 

 large navies are shoaled by dangerous sand-bars.' 



