FOREST IN RELATION TO AGRICULTURE 487 
to come out in the springs of a forest. This also to some extent 
accounts for the saying that if the wells are full in October in the 
Temperate Zone, or at the end of March in the Tropical Zone, there 
will be sufficient water the whole year round. With a varied dis- 
tribution of forests in the country, the above two effects are naturally 
felt on neighbouring agricultural land, and in many cases make 
possible the growing of certain crops, such as cocoa, Cola and rubber, 
which otherwise could not be attempted. An interesting example 
of this is seen in the way in which the natives of Ilobe, in Nigeria, 
have planted Cola trees just inside and on the edge of the Ilaro Forest 
Reserve boundary. 
3. The forest protects the land against corrosion. In most 
countries, wherever the ground is sloping and bare the annual fall 
of rain washes away large masses of good soil as well as stones and 
other debris, in many cases destroying pasturage or agricultural 
land, and in any case silting up the rivers with sand-banks and bars, 
thus hindering navigation. It has often been said that, for its size, 
the Cross River carries in the rainy season much more material in 
suspension and rolled along its bed than many other African rivers. 
The main reason apparently for this fact is that several of its tribu- 
taries, such as the Mbu, the Fi, the Mfu and the Bago, rise at what 
are now partially grass-covered mountain slopes, but which no doubt 
were a short time ago covered with fine evergreen forests. 
The immediate effect of clearing such slopes is that the water, to 
the extent of nearly 90 per cent., rushes unchecked down the mountain 
slope, gaining momentum with every mile and taking grass, soil and 
even whole mountain slopes (1,500 feet in height) along with it. On 
the other hand, if such slopes are covered with forest trees 25 per cent. 
of the rainfall is re-evaporated into the air before reaching the ground, 
10 per cent. is evaporated from the ground into the air of the forest, 
and fully 65 per cent. soaks into the ground. 
An instance of this last effect can be seen in the Cross River Divide 
from the Bambuto Mountains, on the Nigerian border. In a few 
places the native farmers understand this effect and make the 
terraces on which they plant parallel with the contour of the hill-side ; 
however, this is insufficient when the whole mountain slope has been 
cleared of forest. Only a definite distribution of the land between 
forest and farm would prevent the undue corroding of hill-sides. The 
unrestricted rush of the rainwater off the hill-sides has yet a further 
effect on the lower ground of the country, in that it causes the streams 
and rivers to flood and overflow their banks. This, in turn, prevents 
huge acreages of land from being cultivated for many months in the 
year, and other large areas lower down from being cultivated at all. 
Yet another effect is that a vast mass of water hurries down into 
the sea where it is not required, and where there is already plenty of 
