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mineral matter, combined with water by the medium of an acid. 
Petroleum he supposed to be formed by the addition of a calcareous 
earth to the naphtha, dissolved and retained by its acid part. From 
the further combination with earth he supposed that maltha was 
produced ; and by the exsiccation of this, asphaltum. 
Monsieur Tingry, in his observations on some extraneous fossils 
of Switzerland*, considers the detritus of organized bodies, buried 
in the earth, to be the true matrix of the dilferent liquid and 
solid bitumens ; believing that these organized bodies are made 
to assume those characters which distinguish them, more or less, 
from the substances from which they originated, by the influence 
alone of mineral vapours^. He supposes the different states of 
hardness, tenacity, or fluidity, which characterize coals, maltha, 
petroleum, &c. to be entirely the consequence of spontaneous de- 
compositions, and new combinations, effected by mineral vapours, 
and particularly by a certain quantity of water. These substances 
he supposes to thus undergo, during the revolution of ages, and in 
the silence of nature, an analysis similar to that which takes place 
in closed vessels : becoming heated in consequence of their slow 
decompositions, and new combinations ; and thus being resolved 
into coal, which frequently manifests the form, or at least the cha- 
racteristic marks, of organized bodies J. This operation he supposes 
is, beyond doubt, accelerated by the presence of certain mines of 
iron ; since he observes that Derbyshire furnishes a mixture of iron 
and manganese, which takes fire spontaneously on being moistened 
with linseed oil. Subterranean fires, he therefore conjectures, may 
be produced by the mixture of oil of petroleum, with a similar ore 
of iron with that just mentioned. 
* Transactions of the Linnaean Society, vol. i. p. 57. f Id. p. 59. id. p. 60. 
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