OBJECTS AND METHODS OF 
GEOLOGY. 
1. Geology is the Science which treats of the composition 
and structure of the exterior crust of the earth ; the changes 
that are now proceeding in it ; its condition in the most an- 
cient times ; and the causes by which its existing form and 
the present distribution and position of the materials of which 
it is composed, have been produced. 
The great mass of the earth lying within the exterior crust is 
not neglected, but the knowledge we have of it is very limited. 
The objects and methods of this science are more fully explained 
in the two following sections. 
2. The different parts of the earth's surface are unlike each 
other. Some countries are spread out into level plains, and oth- 
ers roughened with hills or studded with mountains, whose tops 
rise above the clouds. If we descend from its exterior form and 
moulding to the characters of the soil and the constitution of the 
rocks, we find them equally various and dissimilar. Widely ex- 
tended regions are fertile almost throughout, whilst others are 
covered with sand, and doomed to remain in future what they 
have been from the earliest ages — waste and trackless deserst. 
Indostan and Arabia, advancing from the continent of Asia into 
the southern ocean, do not differ greatly in size, the former being 
by about one-fiffh part the larger of the two: their latitude, and of 
course their climate, so far as that depends upon nearness to the 
sun, is about the same. Arabia yields a scanty subsistence to a 
population of ten millions, whilst the soil of Indostan sustains 
not less that twelve times that number. The sand hills and mid- 
dle or back country of North Carolina, furnish an example nearer 
home. The mineral riches of the earth's crust are not less un- 
equally and irregularly distributed, than the causes of productive- 
ness and sterility. Limestone abounds in the state of Tennessee ; 
only a few small beds of it have been observed in North Carolina. 
The mountains of Pennsylvania contain coal enough to supply 
the United States with fuel for ages. New England is nearly 
destitute of this valuable mineral. For several years, about the 
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