436 



Miscellaneous. 



fluid, which almost instantaneously evaporates ; this fluid has the 

 smell and all the properties of coal naphtha. The great difference, 

 therefore, in the formation of wood and mineral coal is, that in the 

 production of the former, carbonic acid is evolved ; in that of the 

 latter a hydrocarbon. Hence it is that no combustible gases exist 

 in the mines of wood coals, whilst they abound in those of mi- 

 neral. 



But be this as it may, our conclusion is still the same : that dur- 

 ing the formation of the carboniferous deposits, much carbonic acid 

 was abstracted from, and much oxygen furnished to the atmosphere. 

 From the very low numbers which we assumed as indicating the 

 weight of coal in the carboniferous strata, we have seen that its con- 

 version into carbonic acid would nearly double the quantity of that 

 gas now in the atmosphere. But the marine plants, which probably 

 abounded in the same proportion as the terrestrial, have left few evi- 

 dences of their former existence. They are so perishable in their 

 nature, and surrounded by an element which aids their decay, that 

 their preservation was highly improbable. But during their decay, 

 the carbonic acid from which they were formed, must have been 

 given to the surrounding water; and probably entering into chemi- 

 cal combination with some of its materials, was not again restored to 

 the atmosphere. From whence came all the carbonic acid in the 

 limestones not formed by the accumulation of shells ? some of it, 

 certainly, may have been derived from the source just mentioned. 

 Nor are we to allow ourselves to be misled by the belief that the 

 quantity of carbonic acid evolved from such a source, would be too 

 small to exercise an appreciable effect. The decomposing organic 

 matter has perceptibly affected the whole mass of the ocean in its 

 vast extent ; for all the recent analyses of sea water prove the pre- 

 sence of sulphuretted hydrogen — a gas only generated by the action 

 of decomposing organic matter on salts of sulphuric acid. There are 

 salts of lime in sea water, particularly the sulphate of lime, now 

 this salt is very easily decomposed by a carbonate. Supposing that 

 during the decay of the marine plants, which every analogy leads us 

 to suppose must have existed in quantity proportional to the terres- 

 trial, an alkaline carbonate was produced; this acting upon the 

 uulphate of lime would occasion a precipitation of carbonate of lime, 

 and give rise to those soluble alkaline sulphates, which we find in 

 such quantity in sea water. By this suggested explanation, J by no 

 means infer that this was a general mode by which the stratified 

 limestone was produced : the undivided limestone could not possibly 



