CAPABILITIES WITH REFERENCE TO SETTLEMENT. 317 

growth of plantations, and a similar effect, coupled with the increase of 
springs in number and volume, has been noticed in France, South 
America, Australia, Madeira, St. Helena, and other countries.* 
743. A country clothed with arboreal vegetation is, to a great 
extent, protected from denuding agencies, by the mat of vegetable soil 
with which it becomes covered. The shade afforded by the trees, also 
prevents the too rapid abstraction of moisture from the soil, and it 
is accumulated in the subsoil, and the supply of springs and rivulets 
regulated and maintained. The precise manner, however, in which a 
mantle of trees acts, in causing increased precipitation, is not so well 
known. The foliage, no doubt, tends to retard and arrest currents of 
air, and by lowering the temperature of the stratum nearest the earth 
causes the formation and growth of clouds. It would appear, however, 
that a great part of the influence is of a more subtle nature, and depends 
on the electrical state of the air and earth. Mr. Fryer evidently inclines 
to that opinion. Trees rooted deeply in the damper layers of the soil, 
and ending upwards in innumerable conducting points and edges, must 
tend silently to neutralize the differently electrified air and earth, and 
relieve that state of tension, which, when it exists in the former, causes 
the repulsion of the aqueous particles, and prevents their coalesence and 
precipitation. The prairie grass when it is green and fresh, may, to 
some extent, have, in this way, the same effect as trees; but it is at once 
apparent, that a hot and parched surface, whether of rock or sand, or dry, 
withered grass, must not only not attract rain, but actually tend to repel 
it, and prevent the precipitation of the moisture existing in the atmos- 
phere. Last year, on the second prairie steppe, I noticed the formation of 
clouds over the broken and wooded area, known as Turtle Mountain, 
which, though it may have been brought about in some measure by its 
elevation, seemed to be caused chiefly by its forest-clad surface. The 
wind was fresh, and blowing from the south-south-east. and though the 
whole sky was hazy, with light clouds, a persistent cloud-cap seemed to 
form over the higher wooded area, and tail away towards the north, 
some light showers falling upon the mountain at the same time. 
744. The Great West of America is too new to have yet accumulated 
many facts from experience, but in several directions, encouraging results 
have already been observed to follow the advance of settlement, and the 
planting of trees. ‘“ When the Mormons first settled in Utah, they found 

*See Fryer, loc. cit. 
