256 
the distance apart depending upon the nature of the land and the 
slope of the surface, as in case of sidehill ditches. Theoretically, 
it is intended to have the surface between these two furrows level 
so that there will be no chance for the water to run off over the 
surface. On a small scale this levelling can be done with a horse 
shovel, and the land thus put once into a condition to prevent 
washing. In this case the banks of the terrace are sodded or seeded 
with grass to prevent them from washing. In the field practice, 
however, the soil is moved gradually with a plough, the furrow be- 
ing thrown always downhill and the soil gradually worked down to 
a level plain. There are several forms of reversible ploughs which 
are admirably adapted to this purpose, being turned readily from a 
right to a left handed plough, so that in going back and forth the 
furrow is always thrown downhill. If requires, of course, a num- 
ber of years of such cultivation to get the surface into even approxi- 
mately a level condition, but with patience and thorough cultivation 
the soil very quickly assumes a comparatively level aspect and 
erosion is reduced to a minimum. This is a more expensive method, 
but if intelligently done it is much more efficient and much more 
durable than depending upon sidehill ditches to prevent erosion. 
As was said in the case of the sidehill ditches, unless this work is 
well done it had much better be left undone, as it may seriously 
injure the field. 
Where erosion has proceeded so far as to render the land at pre- 
sent unfit for cultivation, or where the land is not needed for cul- 
tivation and it is desired to prevent erosion, the land should be 
given up to trees, herbs, or grasses of some kind according to one 
or other of the following methods. 
Recovering Gullied Hillsides bv Reforestation. 
Forest ground is not subject to this erosive action of the rainfall 
because in a forest a large part of the rainfall never reaches the 
soil, as 20 or 30 per cent, is intercepted by the foliage and eva- 
porated before it reaches the ground. The rainfall which reaches 
the surface is rapidly absorbed, as the soil is kept granular and 
loose and much more of the water is carried off by underdrainage 
rather than by surface drainage. 
The forest covering protects the soil in the 
FOLLOWING WAYS. 
1. By preventing rain from tailing directly upon the soil, the 
foliage of the tree crowns intercepting and breaking its force, the 
water reaching the soil more gently from the leaves and along the 
branches and trunks of the trees. 
2. By interposing a loose cover or mulch of litter formed by 
the fallen leaves and'branches, which breaks the direct force of the' 
raindrops and keeps the soil from being compacted or puddled by 
their blow. 
t .. The deeply penetrating roots, and holes left from decayed 
stumps and roots of trees, assist in this underground drainage. 
