INJURIOUS EFFECTS OF DISAFFORESTING LANDS. 115 



Agriculturalists also tell us of the marked effect 

 exercised by drainage, which enables the heat of the 

 sun to penetrate more deeply into the soil. Works 

 upon the science of agriculture are unanimous in pointing 

 out that by draining away the surface waters which 

 saturate the soil, a vast improvement is effected, on 

 account of the known fact that water is an exceedingly 

 bad conductor of heat. 



It is probable that the influence of human agency 

 in the modification of climate is nowhere more clearly 

 or strikingly exhibited than in the act of disafforesting 

 the earth's surface. The length of the northern winter 

 is curtailed, and its rigour diminished. On the other 

 hand, the intensity of the tropical heat is increased 

 by the removal of shade the droughts are prolonged, 

 the rainfall lessened, and the process of erosion which 

 we have spoken of in connection with the formation 

 of canons and other denudations of the soil, by tor- 

 rential rains, is enormously and destructively in- 

 creased. 



It would be too long to enter into this question at 

 greater length; the records of the island of St. Helena 

 however, conclusively show the injurious effects of the 

 removal of the forest there. When this island was 

 first discovered by the Portuguese, in 1502, it was 

 covered with a dense growth of luxuriant forest, and 

 possessed a soil of remarkable fertility, which now, 

 since the removal of the trees, presents an aspect of 

 sterility so great 



" that it is difficult to believe that it was once green and 

 fertile. When the vegetation was destroyed, the heavy tropical 

 rains washed away the soil, and left a vast expanse of bare 

 rock and sterile clay. This irreparable destruction" (we are 



