WIND EROSION 131 
known from the frequent descriptions of them by travy- 
ellers in the Sahara, where they sometimes endanger life. 
Sand Dunes. — By this process the fine particles are 
drifted about, and in places where the drift accumu- 
lates, sand hills or sand dunes are built (Fig. 59). The 
soil of the surface is in such frequent movement, 
that even the desert plants cannot find a foothold. 
Fig. 59. 
The desert of Sahara. Practically no vegetation. Sand dunes in the background. 
Extensive deposits of sand and clayey sand are some- 
times made in these places; and in parts of northern 
China, deep deposits of such & wind-blown soil, called 
loess (Fig. 60), dover a wide area. Of course all these 
deposits are fine in texture, never being coarser than 
sind, because the wind can carry only the lighter bits 
of rock. 
