SOIL EROSION IN THE SOUTH. 11 
water. The most effective methods make use of both principles. 
The porosity of the soil may be increased by the incorporation of 
organic matter and by breaking the soil to considerable depth. Deep 
plowing alone is not so beneficial as when used in conjuction with the 
incorporation of organic matter in the soil. The organic matter 
promotes a granulation of the soil particles and thus produces a soil 
with larger spaces between the soil granules. The rate of absorption 
is greatly increased and the storage capacity enlarged. 
Tillage operations which move the soil to considerable depth tend to 
lessen erosion. They furnish a larger reservoir for the reception and 
retention of water. Preliminary experiments in this laboratory 
indicate that the dust mulch may have no advantage and is, possibly, 
a positive disadvantage. The fine particles of dust, when sub- 
jected to a sudden shower, are beaten into a thin layer of puddled 
soil on the surface which prevents rapid absorption and allows water 
to flow off the surface of the soil. 
The methods that decrease the velocity of the running water are 
those in which impediments are placed in the path of the run-off. 
For every given velocity of running water there is a maximum amount 
of material that can be carried in suspension, and this amount in- 
creases with the velocity. If, then, flowing water carrying its maxi- 
mum load has its velocity reduced it becomes overloaded and must 
deposit part of the load. If the velocity remains low the carrying 
power of the water is small. With the methods intended to check 
the velocity of the water belong the construction of various forms of 
terraces and the growth of vegetation or the placing of any impedi- 
ments in the path of the water. 
LAYING OFF TERRACES. 
Terraces, no matter of what kind, should be laid off level or 
nearly so. The most common way is to use a leveling instrument 
and a rod with target attached. In laying off the terrace, the instru- 
ment is set on the highest part of the land and the bubble brought to the 
middle of its tube. The rod is placed by the level and the target moved 
to a height 3 feet above the line of sight. The rod should then be 
moved downhill until the target is in the line of sight. The bottom 
of the rod will then be 3 feet below the position of the level. Other 
points at the same level, 10 or 15 paces apart, should be located and 
through these points the terraces constructed. After the line of one 
terrace is located, the level may be set upon one of the points marked, 
proceeding as before. The terrace lines will then follow the contour 
of the hills. If slight depressions occur between two points, it is 
best not to change the terrace line, but to fill in the depression. 
Instead of using a level, good results may be obtained with an imple- 
