THE WEATHERING OF ROCKS 313: 
XVI.—THE WEATHERING OF ROCKS. 
By the term weathering is meant the effect which all 
kinds of meteoric action have upon the superficial parts of 
rocks, causing a disintegration of the surface, and a 
loosening and crumbling of the stone. 
Effects of heat and cold. Heat causes rocks to expand, 
cold causes them to contract. The amount of contraction 
and expansion, moreover, varies considerably with different 
minerals. In many countries—notably in certain parts of 
our own—the daily and seasonal changes of temperature 
are considerable. Hence, in all rocks exposed to the sun’s 
rays, there is constantly taking place an increase or 
diminution of volume, by the expansion or contraction of 
some portions more rapidly than others: this has the 
effect of gradually tearing apart the constituents of which 
the rock is composed. The surface is connected with a 
loose crumbling crust, which tumbles off and subsequently 
undergoes further disintegration. The cracks and fissures, 
with which the mass gradually becomes traversed in all 
directions, form passages for the admission of air and water, 
which further assist in the process of weathering. 
Effects of frost. Almost every known substance 
diminishes in volume as its temperature is lowered. This 
is true of water, as it cools from boiling point to 4° C.; at 
this temperature, however, it begins to expand, and, at the 
moment of its conversion into ice, its volume increases to 
such an extent that nine cubic inches of water become 
about ten of ice. The force developed by this expansion is 
well nigh irresistible, so much so that strong steel vessels 
filled with water and closed by screw stoppers have been 
burst by it. In this way, the water freezing in rock- 
crevices is able to force their sides further apart, and carry 
the fissures deeper into the rock-mass. Pieces, both large 
