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It is reasonable to conjecture, he thinks, that the remains of 
vegetables, accumulated in large heaps, and exposed to the effects 
of those particular combinations which occasion the heat of certain 
mineral waters, or to the influence of volcanic fires, may have un- 
dergone a real distillation; and that the substances thus formed, 
meeting with water which impeded their further decomposition, 
have been carried to the surface of the earth, and appear there 
under the form of naphtha, &c. Under other circumstances, he 
conceives, that these same oils, thus detached by distillation from 
the wood, have filtered insensibly into the beds of sand and clay, 
and thus have produced the formation of coal and bituminous 
schisti ; whilst, under other circumstances, these oils, accumulated 
in the interior cavities of the earth, have assumed the consistence 
which we observe in mineral pitch. 
To the opinion of Mons. Tingry, respecting the gradual decom- 
position of vegetable matter, I certainly cannot object ; but later 
observations, and particularly those of Mr. Hatchett, have clearly 
demonstrated, that, however difficult it may be to account for the 
different states in which the bitumens are found to exist, the action 
of subterraneous fires, and the operation of distillation, cannot have 
been the agents which have occasioned those varieties, in the forms 
under which these substances appear to us. It may be proper to 
remark, with respect to this supposed influence of subterranean 
fires, that Dr. Hutton, and many of the French chemists, have 
adopted the same idea, and to as considerable an extent. 
Dr. Darwin was of opinion, that morasses seem to have under- 
gone a fermentation ; but that the formation of coal depends on a 
distillation similar to that which is supposed by Dr. Hutton. The 
Doctor says, that “ woods in uncultivated countries have grown 
and fallen through many ages, whence morasses of immense extent ; 
or, as he expresses it. 
