8 FORESTS, WOODS, AND TREES 
remembered that when there occur abnormally heavy 
precipitations or long-continued rains, the forest floor will 
become saturated and be unable to absorb more water, so 
that disastrous floods may occur even in the best forested 
areas. The forest, however, plays an important part in 
preventing a certain proportion of the otherwise inevitable 
floods ; and its effect on the supply of water to springs is 
undoubted. Forests are efficient to a high degree in pre- 
venting erosion of the soil, formation of torrents, disastrous 
floods, and the filling up of the beds of rivers with silt. 
In channels filled with sediment even a slight rainfall may 
cause a flood, hence the utility of the forest in keeping 
streams and rivers deep and capable of carrying away 
unusual quantities of rain. 
The effect of deforestation in increasing the number and 
seriousness of floods was well shown by M. O. Leighton (6) 
in 1909, who proved that floods in the United States had 
been increasing in most rivers, no other cause being dis- 
cernible than the continuous felling of timber in the upper 
part of their watersheds. 
It is the absorbent nature of the ground that determines 
whether or not a larger or smaller proportion of the rainfall 
and snow will run off directly into the river. A large 
proportion is a flood. None of the conditions in the river 
basins studied by Leighton appeared to vary, except the 
surface vegetation, as the climate, topography, geology, etc., 
remained unaltered. The variation in the surface vegetation 
was the continuous reduction of the forest area by felling 
timber in the river basins. The watersheds studied were 
those of three tributaries of the Ohio River in its upper 
drainage area. During the last 20 to 30 years, there was 
an increase of floods; and when the variation in the annual 
rainfall has been allowed for, Leighton’s diagrams show that 
the only factor that could have had any influence in 
increasing the floods was the constant and rapid deforesta- 
tion that had been carried on during the period in the 
three river basins. 
Hall and Maxwell (7), who studied the conditions of 
