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The excerpt represents the core issue or deciding factor on which you must meditate, and is drawn from Madam How and Lady Why by Charles Kingsley: lately only used for common farmers' crops.
But how do they turn Coprolites into manure? I used to see them
in the railway trucks at Cambridge, and they were all like what I
have at home--hard pebbles.
They grind them first in a mill. Then they mix them with
sulphuric acid and water, and that melts them down, and parts them
into two things. One is sulphate of lime (gypsum, as it is
commonly called), and which will not dissolve in water, and is of
little use. But the other is what is called superphosphate of
lime, which will dissolve in water; so that the roots of the
plants can suck it up: and that is one of the richest of manures.
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