AGENTS THAT DESTROY ROCKS 133 
tor just as we now behold them; but those who 
have followed us thus far will have seen that such 
a conclusion must necessarily be erroneous. The 
remains of animals and vegetables imbedded in the 
solid rock, thousands of feet beneath the surface, 
must have led them to conclude that such rocks 
were formed after the animals and vegetables con- 
tained in them had existed ; and, in short, that rocks 
are produced by agents similar to those that are 
now exerting their influence upon the surface of the 
^ globe. But, in order to show how rocks are con- 
tinually forming at the present time, we must first 
point out how they are destroyed ; for it is by their 
disintegration and decomposition that materials are 
furnished for new formations. 
Slight observation teaches us that the surface 
of the earth is everywhere undergoing important 
changes. The hardest rocks are broken down and 
decomposed, and a variety of causes are aiding in 
this work. Although, to the casual observer, the solid 
inorganic world seems to be steadfast and immo- 
vable, yet the earth is constantly taking new states, 
even beneath his own feet. The effects, it is true, 
may be gradual or almost imperceptible, but they 
are none the less certain or efficient. Every stream 
. or river which flows through our country bears along 
a greater or less proportion of mineral substances ; 
which, being carried into the sea, are again thrown 
by the waves upon the beach, thus forming a sandy 
soil like that of New-Jersey or on the eastern side 
of Long Island. 
Rocks suffer disintegration frony three different 
causes, namely: 1. Mechanical A^nts ; 2. Chemi- 
cal Action ; 3. The Freezing and Thawing of Water, 
I. Mechanical Agents which Destroy Rocks. 
Water, in its influence upon rocks, may be justly 
considered as a mechanical agent, although, to a 
certain extent, it is a chemical one also, as it has 
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