EFFECT OF SETTLEMENT UPON INDIGENOUS VEGETATION. 193 
“The fall of rain in any district increases with the increase of 
vegetation, and especially of forest growth. Trees and forests 
contribute to the formation of springs and watercourses, not only 
by means of the humidity which they produce, and the condensa- 
tion of vapours by refrigeration, but also by reason of the obstacles 
which they present to the evaporation of the water in the soil 
itself, and by means of the roots which, by dividing the soil like 
so many perforations, render it more permeable and facilitate ~ 
filtration. The clearing of forests and the consequent drying up 
or draining of marshes and bogs, have caused a material alteration, 
not only in the entire face of the country, but in the supply of 
water to the rivers, formerly derived from these resources, and in 
the periodical amount of rainfall and the regularity of its distri- 
bution. In Germany it is considered that, in order to secure a 
regular and sutficient rainfall in agricultural districts, the propor- 
tion of forest or woodland shalJl not be less than twenty per cent.”* 
Humboldt too, who first broached the theory, was of opinion 
that forests influence rainfall. Buff says: “‘The Canary Islands, 
when they were first discovered, were clothed with thick forests, 
and overgrown with the richest verdure. Great part of these 
woods were destroyed and burned by the first settlers ; the result 
has been the lessening of their rains, and the dwindling away of 
their springs and brooks.” Thus the rooting up or even the mere 
thinning of forests always exerts a striking influence on the 
moisture of a country. Many districts, which in former times 
were known for their rich fruitfulness, have lost, together with 
their forests, much of their flourishing condition, and have even 
been changed in part into desert. But you will also see that, by 
gradually planting trees, many regions of our earth, which have 
been hitherto waste and barren, may be rendered fit for tillage 
and the dwelling of man,” + 
Speaking of the Vindhya Range, Sir J. D. Hooker says: ‘The 
climate of the whole neighbourhood has of late changed materially; 
* Prof. J. Scott quoted by 8S. Pollitzer—Sydney Quarterly Magazine, 
Vol. vit., p. 7. 
+ Physics of the Earth. 
M—Sept. 7, 1892. 
