mineral matter, combined with water by the medium of an acid. 

 Petroleum he supposed to be formed by the addition of a calca- 

 reous 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 different 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 -f. 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 ne^ 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 $. This operation he sup- 

 poses 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 con- 

 jectures, 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. t Id. p. 59. $ Id. p. 60. 



