80 Rainfall^ Natural Drainage^ 



and the general result is similar to that produced by the vicinity 

 of the ocean. On the other hand, extensive tracts without wood 

 are always dry and parched. Spain is an example of a country 

 that has suffered much from the removal of the forests that once 

 covered it. It is possible now to travel across hundreds of miles 

 of the peninsula without seeing a tree except in the hollows and 

 deep narrow valleys through which the streams run. Trees now 

 refuse to grow on these plains, and it would take many years of 

 careful management to replace the great forests that were once 

 so common. But with the first belt of wood the condition of 

 the climate would no doubt begin to alter. It would certainly 

 be impossible to replace the old forests under the present climate, 

 but the old climate would perhaps be restored if the natural 

 vegetation were allowed to become arborescent or if trees were 

 cultivated. Examples of this may be seen in Scotland, where in 

 several places trees have been planted with very marked and 

 favourable results. Even more striking, however, is the case of 

 Egypt, where at the close of the last and beginning of the pre- 

 sent century rain was a very rare phenomenon, not falling some- 

 times once in twelve months. Since that time Mehemet Ali and. 

 Ibrahim Pacha have planted very freely, to the extent it is said 

 of twenty millions of trees, consisting of olive, fig, cotton-wood, 

 orange, acacia, and plane. Rain now falls, not only on the coast, 

 but in the interior during all the winter months. 



Forests affect the supply of water to springs as well as induce 

 a larger quantity of rain over a given surface. This arises from 

 the protection they provide against evaporation, and the time 

 thus afforded to the moisture to penetrate beneath the surface. 

 In America cases are recorded where springs have greatly and 

 steadily decreased after the clearing of land, and Mr. Marsh, in 

 his recently published work on ' ?vlan and Nature,' states : — 

 " I remember one case where a small mountain-spring, which 

 disappeared soon after the clearing of the ground where it rose, 

 was recovered, about ten or twelve years after, by simply allow- 

 ing the bushes and young trees to grow up on a rocky knoll not 

 more than half an acre in extent immediately above it, and has 

 since continued to flow uninterruptedly." In South America, in 

 the valley of Aragua, in Venezuela, there was a town founded 

 in 1555 half a league from a lake, the surrounding country being 

 then clothed with forest. The forests were cut down, and in the 

 year 1800 there had been for 30 years a large population on 

 the spot. It was then visited by Humboldt, Avho found the 

 town about two miles further from the lake than it had been, 

 owing to the diminution of the water supply. Twenty-two years 

 later political events had caused the reduction and removal of 

 the population, and the forest had grown once more. The 



