243 
In the hypothesis of Mr. Kirwan, the most obvious difficulty 
seems to be in admitting the prompt subsidence of the finely divided 
particles of so light a substance as bitumen, through the w^aters of 
the ocean. Mr. Kirwan supposes the carbonaceous, as well as the 
bituminous particles, to be separated by the disintegration of the 
antediluvian mountains ; and then to enter into reunion, and suffer 
a precipitation through the water. Such a combination I have 
endeavoured to prove is constantly taking place, in every case 
where the thickening of the substance and the darkening of the 
colour, of any bituminizing substance is going on. Thus, in con- 
sequence of the addition of oxygen to the thin and limpid naphtha, 
a combination of that principle with the carbon ensues ; and the 
fluid becomes thicker and darker, assuming the form of petroleum. 
Bv a continuance of this process, these^ effects are produced in a 
still higher degree, and the hard, dark bitumen, asphaltum, or the 
still more highly carbonaceous bitumen, jet, is formed. But every 
one of these substances, we perceive, are of such a degree of spe- 
cific gravity, when pure, as not to allow us to assume the possibility 
of their sinking through the moist, pulpy, argillaceous mass, as Mr. 
Kirwan describes it : neither could it possibly be admitted, even if 
such a subsidence were granted, that such materials should form, as 
Mr. Kirwan also conjectures, the lowest stratum. 
Wlulst on this subject, I must make one more observation, which 
appears to me very forcibly to conffadict this supposition of the 
formation of coal by deposition. The specific gravity of the sub- 
stances forming the roof of coal, constantly exceeds in a very .high 
degree, that of the bituminous mass they cover; they containing 
very frequently so much metallic matter as to render them exceed- 
ingly ponderous. Now the disintegration, of which Mr. Kirwan 
speaks, he supposes to have been so complete, as to have converte 
the hard and close-grained hornblend and felspar into clay. By so 
