124 ELEMENTARY GEOLOGY 
-. In arid countries (Fig. 57), where the soil is dry and 
vegetation scanty, the wind sweeps over the land, 
and in some cases blows the soil from the rocks, leay- 
ing them constantly bare to the attack of the weather. 
Formation of Talus. — Where cliffs rise, as they do 
near many streams, small particles fall from the rock 
and drop to the 
base. As these 
accumulate, they 
form a deposit of 
angular — debris, 
called talus (Fig. 
58). Sometimes 
the talus is very 
small, while in 
other cases it 
reaches well up 
Fic. 56. on the sides of 
A part of the Adirondacks near Lower Au Sable the eliff. As it 
Lake, showing a surface protected by heavy forest. 
(Copyrighted, 1889, by S. R. Stoddard, Glens Falls, grows upwards, 
ret it protects the 
rocks from further rapid decay; but before this, the 
naked rock face, constantly exposed to the weather, 
and kept bare by the aid of gravity, is a place of 
rapid rock waste. 
Difference in Rate of Weathering. — There is a wide 
difference in the rate at which rocks weather under 
