241 
most probably, a far larger proportion of carbon and petrol, than . 
those of the same denomination now contain, since their disin- 
tegration took place at so early a period.” 
On this supposition, Mr. Kirwan proceeds to say, “ I think the 
formation of coal-mines, and most of the circumstances attending 
them, may naturally be accounted for. 
“ And, first, as to the seams of coal themselves, and their at- 
tendant strata ; they must have resulted from the equable diffusion of 
the disintegrated particles of the primitive mountains, successively 
carried down by the gentle trickling of the numerous rills that 
flowed from those mountains, and in many cases more widely dif- 
fused by more copious streams. By this decomposition, the felspar 
and hornblend were converted into clay ; the bituminous particles, 
thus set free, reunited, and were absorbed, partly by the argil, but 
chiefly by the carbonaceous matter with which they have evidently 
the greatest affinity; since they are separable by boiling water 
from the former, and scarcely, by the strongest heat in close vessels, 
from the latter; and even in an open fire, only by a heat much 
superior to that of boiling water. The carbonic and bituminous 
particles, thus united, being difficultly miscible with water, and spe- 
cifically heavier, sunk through the moist, pulpy, incoherent, argilla- 
ceous masses, and formed the lowest stratum, unless in cases where 
their proportion to the argillaceous particles was so small, that the 
latter had subsided and coalesced, before the former could have 
been reunited ; in that case the clayey particles formed the lower 
stratum of indurated clay. But if the petrol were in the greatest 
proportion, it frequently sunk first, in the form of a soft bitumen, 
carrying with it the clay, and forming beds of shale, or bituminous 
shale, according to its proportion. By oxygenation it becomes spe- 
cifically heavier than water*.” 
WOL. I. 
* Geological Essays, p. 330. 
II 
