56 PRACTICAL FORESTRY 
corroded and comminuted, that is, diminished in 
size—a process which does not injure fine soils con- 
taining an abundance of humus, because by its pres- 
ence the proper degree of capillarity is assured, but 
which decidedly improves coarse soils by removing 
their greatest drawback, which is excessive porosity. 
In short, the presence of the proper kind of humus 
is a great benefaction to all grades of soils. The 
greatest source of the best kind of humus is the hard- 
wood forest. 
3. Tur Forest as A Sort-Frxer 
One of the most important functions of the forest 
is the fixation of soil. The roots of the forest clasp 
and hold the soil in place, and the mulch and canopy 
of the forest protect it to such an extent that wind 
and water erosion are prevented. Erosion is the wear- 
ing away of rocks and soils by the action of both 
water and wind. 
In many parts of the world the wind blows the 
sand into shifting masses called dunes. In many in- 
stances, especially along the ocean, these shifting 
dunes have buried villages and fertile farm-lands. 
Dunes have been fixed or rendered stable by the plant- 
ing of forests. In Gascony, in the southwestern part 
of France, the sands from the ocean rendered vast 
areas desolate and uninhabitable. ‘To-day they are 
