omOIN OF COAL, 



111 



their substance, or 44 of carbonic acid to 56 of lime. Now, the 

 quantity of carbon, when separated from the oxygen, would be equal 

 to one eighth of the whole mass of limestone ; and, as all the an- 

 cient limestone formations were deposited under the ocean, we can- 

 not suppose that diis carbon was derived from the vegetable king- 

 dom, ('ould die carbon be separated from the limestone in the 

 great calcareous raiiges of the Jura and the Alps, it would form a 

 bed of pure carbon, nearly a thousand feet in thickness^ through the 

 vast extent of these mountains : and were we forced to admit that 

 this carbon was derived from organic secretion, vi/e should rather 

 look to the animal than the vegetable kingdom for its origin ; as no 

 small portion of many calcareous mountains is composed of ani- 

 mal remains, and calcareous beds are forming in our present seas, of 

 great extent and thickness, by the accumulation of shells and coral. 



M. Adolphe Brongniart, in a recent work on vegetable fossils, has 

 ingeniously suggested another origin for vegetable carbon i he ad- 

 mits, as I have done, that carbon is an original element in the compo- 

 sition of the globe, and its atmosphere. He supposes that the at^- 

 mosphere of the ancient world, might contain more carbonic acid 

 than at present. This would be highly favorable to the rapid growth 

 of plants ; and, in propordon as the plants absorbed the excess of 

 carbonic acid (fixed air), they would render the atmosphere more 

 pure, and fit it for the future respiration of animals. 



Bitumen, which is composed of carbon and hydrogen, is knowo 

 to exude from the lava of recent volcanoes ; and the volcanic tufa io 

 Auvergne, which covers a vast extent of surface, is, almost every 

 where, intermixed with bitumen. In hot v^^cather I have seen it 

 trickling out of the tufa in considerable quandties, resembling melted 

 pitch. As the ancient volcanoes of that district broke out from be- 

 neath the granite, we may fairly infer, that the bitumen which abounds 

 in the volcanic tufa is as much a mineral substance as the sulphur 

 which accompanies volcanic eruptions, or which is sublimed from the 

 vapors of quiescent volcanoes. 



Though the carbon that exists as a constituent part in some pri- 

 mary rocks may be derived from the mineral kingdom, there can 

 scarcely remain a doubt, that ivood-coal and common coal are of 

 vegetable origin. Wood-coal, or brown coal, is found in low situa- 

 tions, and appears to have been formed of heaps of trees buried by 

 inundations under beds of clay, sand, or gravel The woody parts 

 have probably undergone a certain degree of vegetable fermentation, 

 under the pressure of the incumbent earthy matter, by which they 

 have been carbonized and consolidated. In some specimens of this 

 coal, the vegetable fibre or grain is perceptible in one part, and the 

 other part is reduced to coal. The vegetable principles which this 

 coal contains, united with bitumen and charcoal, have been already 

 stated. In black or common coal, the vegetable extract and resin 

 are destroyed, and the charcoal and bitumen alone remain ; but 



