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 instances, 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 that of Bovey, is also observ- 
able. Impregnation of the earth to a considerable thickness 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 discharges itself into the 
lake Palius ; and the earth above it, even to the surface, 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 proportion 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 impregnated by the fluid bitumen, whilst the 
coal existed in the fluid state of petroleum. 
blast was applied, than a similar quantity of air, urged 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 principles of the latter, into an intermediate gaseous 
state ; in which the two principles, being less closely united, would act on their application to 
the burning embers, with energies 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. 
* Nicholson’s Journal, April, 1801. 
