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The specific gravity and hardness of some species of coal, have 
procured coal in general to be distinguished, by some, by the term, 
stone-coal. Struck by the predominance of these qualities, and 
perceiving also the great quantity of bituminous matter contained 
in coal, this substance has been considered, by some chemists of 
considerable knowledge and abilities, as being an earth, or rather 
a stone of the argillaceous genus, which has become impregnated 
with petroleum. The impropriety of thus considering it must, 
however, at once appear, when it is recollected, that chemical ex- 
amination has shown, that, in common coal, the proportion of earth, 
to that of carbonaceous and bituminous matters, is so very trifling, 
as seldom to exceed a thirtieth part of the mass. 
In some instances, indeed, such as the slaty cannel coal, from 
Ayrshire, in Scotland, analyzed by Mr. Kirwan, and the stony coal 
of Macinaia, the analysis of which has been given by Signor Fa- 
broni, the earthy parts have amounted to a fifth, and even one half 
of the whole mass. But these are substances which deviate so 
much from the characters of coal, as not to be admissible into the 
same class with it, but should be rather considered as varieties of 
slate, lime-stone, &c. 
Others have been of opinion, that coal is entirely of marine 
origin ; and formed by the fat, and various unctuous matters, which 
have proceeded from the innumerable tribes of animals which have 
peopled the ocean. This mass of matter is supposed to have ac- 
cumulated, and at last to have been covered by various strata, in 
consequence of the different changes which the surface of the earth, 
and the receptacles of the waters of this globe, have experienced. 
To show the improbability of this hypothesis, it is, perhaps, suf- 
ficient to remark, that the levity of such substances could never 
admit of their accumulation at the bottom of the sea, which, ac- 
cording to the principles of this theory, must be supposed to have 
taken place. 
