98 RELATIONS OF THE EARTH 
those which actually exist. Had the earth's 
surface presented only one unvaried mass of 
granite or lava; or, had its nucleus been sur- 
rounded by entire concentric coverings of strati- 
fied rocks, like the coats of an onion, a single 
stratum only would have been accessible to its 
inhabitants; and the varied intermixtures of 
limestone, clay, and sandstone, which, under 
the actual disposition, are so advantageous to 
the fertility, beauty, and habitability, of the 
globe, would have had no place. 
Again, the inestimably precious treasures of 
mineral salt and coal, and of metallic ores, con- 
fined as these latter chiefly are, to the older 
series of formations, would, under the supposed 
more simple arrangement of the strata, have 
been wholly inaccessible ; and we should have 
been destitute of all these essential elements of 
industry and civilization. Under the existing 
disposition, all the various combinations of strata 
with their valuable contents, whether produced 
by the agency of subterranean fire, or by mecha- 
nical, or chemical deposition beneath the water, 
have been raised above the sea, to form the 
mountains and the plains of the present earth ; 
and have still further been laid open to our reach, 
by the exposure of each stratum, along the sides 
of valleys. 
With a view to human uses, the production 
of a soil fitted for agriculture, and the general 
