260 



A circumstance which respects the roof of coal-pits is well deserving 

 your attention, in this place. Generally the schistose covering, which 

 forms the roof, is, for a considerable thickness, so impregnated: 

 with bituminous matter as to possess a degree of combustibility, 

 which is, in some intances, so great as to allow the employment 

 of these schisti, for the purpose of combustion, in the burning of 

 lime, smelting of metals, c. A similar impregnation of the earth 

 which covers the fossil wood of Munden, and of that of Bovey, is 

 also observable. Impregnation of the earth to a considerable thick- 

 ness is also well known to exist in the earth in the neighbourhood 

 of petroleum springs. Thus, as has been already noticed, in the 

 valley of Noto, in Sicily, is a spring of petroleum, which discharge* 

 itself into the lake Palius ; and the earth above it, even to the sur- 

 face, is so much bituminized, as to have taken fire by accident and 

 to have burned for several months. The connection between these 

 several impregnations appears to be evident. As the resolution of 

 vegetable matter into a bituminous fluid takes place, so in propor- 

 tion will the adjoining earth become impregnated ; and where this 

 change is so complete that a fluid bitumen is formed, the diffusion 

 and absorption will, of course, be extensive, in proportion to its 

 fluidity. The bituminous schist, which is adjoining to beds of 

 coals, is evidently formed of such earths, as have become impreg- 



of the fire to which its blast was applied, than a similar quantity of air, uro-ed with 

 an equal degree of velocity by a bellows of common construction., Might not the 

 agitation and intermixture of the air and water produce a partial separation of the prin- 

 ciples of the latter, into an intermediate gaseous state ; in which the two principles, be- 

 ing less closely united, would act on their application to the burning embers, with ener- 

 gies somewhat similar to those which the two principles exert when entirely separate. 

 Whether it exists in this partially decomposed, but permanent gaseous state, or entirely 

 decomposed into the two original permanent gases belonging to its constitution, as has 

 been supposed to be the state in- which it exists in the atmosphere ', must be left to, 

 future experiment to determine. 



1 Nichoteop'a Journal, April 1801. 



