PRELIMINARY REMARKS. 
9 
miles. Here the total annual fall of rain is approximately 
thirty-six inches. Forty per cent of this quantity passes off in 
the drainage of the branches above Wheeling; sixty per cent 
is evaporated, or is employed by the vegetable kingdom. The 
average discharge of the Ohio at Wheeling for six consecutive 
years, was found to be 835,323,000,000 cubic feet. The quan¬ 
tity of solid matter which this quantity of water holds suspended 
in a cubic foot, is approximately part. 
The quantity of rain which a country annually receives is 
connected with the amount of degradation which that country 
is undergoing; and the amount of matter dissolved out of the 
exposed surfaces of limestone and other rocks, is also related to 
the quantity of rain which flows over its surface. The quan¬ 
tity of carbonic acid and ammonia which is required to confer 
fertility upon a country, stands connected with the number of 
inches of rain with which that country is supplied. When 
observations have been made upon the quantity of rain which a 
given area receives annually, together with the amount of sedi¬ 
ment which drainage carries away, it will be possible to form an 
approximate calculation of the rate the degradation is going on, 
as well as the rate at which the valleys are filling up. There are 
also many other problems which will receive a solution when 
the related facts or data shall have been obtained. 
Questions of a practical kind, and which are closely related 
to geology, are constantly arising; and upon their answer some 
of the most important interests of society are involved. For 
example, our rivers overflow their banks, and inflict heavy 
damages upon private and public property. Can any practical 
scheme be devised, by which these injuries shall be avoided or 
prevented? Can those streams be controlled so far as to render 
their swellings harmless. We have a natural illustration how 
nature sometimes counteracts her own evils: the Androscoggin, 
when in flood, flows through a short cut into Umbagog lake. 
Hence, its waters being partially diverted for a time, finally 
pass down to the ocean harmlessly. In a valuable treatise on 
the physical geography of the Mississippi valley, by Mr. 
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