CHAPTER VI 
WEATHERING 
Denudation.— ‘The rocks are crumbling and the 
earth’s surface is wearing down from various causes. 
This process of land destruction is commonly called 
denudation. In the pages that immediately follow we 
will examine this subject in considerable detail. 
Effect of Climate. —If a rock is exposed to the 
weather, it commences to crumble (Fig. 47 and Plate 3), 
though the rate at which this takes place, depends 
partly on the climate, partly on the kind of rock 
(Fig. 48), and partly on various other conditions de- 
scribed later. The obelisk of Central Park, New York 
City, after standing for 3400 years in the dry climate 
of Egypt, began immediately to decay when placed in 
the damp and variable air of New York. It was soon 
necessary to protect it from rapid and entire destruc- 
tion; for in five years it had altered more than during 
3400 years in Egypt. When it arrived it was a hard, 
granitic rock; at the end of the five years its surface 
had crumbled, and fragments of gravel had accumu- 
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