649 
of Edinburgh^ Session 1865 - 66 . 
seam ultimately attained by this means may be, we should find it 
comparatively pure and uniform in composition. The whole roof 
of superincumbent material, however great its thickness might be, 
would he lifted up in detail, scarcely a particle would be left be- 
hind to attest the act. 
In part (c) we find how this absorptive power may be applied 
with some degree of probability to account for the production of 
certain bituminous shales and impure coals, characterised by their 
homogeneity, and their poverty in vegetable structures. The 
whole process is nearly a repetition of what is supposed to occur 
in the case of coal itself, the only difference being, that in one case 
the absorbing substance is thinly dispersed through a quantity of 
earthy matters, while in the other it is in a concrete form. 
In part (d) I have attempted to show in what manner the 
partial solubility of coal, together with its absorptive power, may 
have affected its physical character. 
It has been supposed that the whole seam has been repeatedly 
turned over by these means, and each time reduced by the separa- 
tion of portions of it, principally in the form of oxygenated com- 
pounds : the losses so incurred, however, being abundantly made 
up by introduced substances. It is, in fact, a continual re-solution 
and re-deposit. 
Now, all these processes going on at an exceedingly slow rate, we 
are quite certain, judging from analogous cases, that ultimately the 
product so attained will cohere in all its parts, and be possessed of 
the utmost hardness and the highest degree of lustre of which its 
constitution admits. 
In the last part (e), I have used these properties of coal to in- 
crease the differences in adjoining parts of the seam. To assist in 
this, and to give a greater completeness to the work, I have gone 
further back in the history of coal, and traced a supposititious origin 
for the commencement of these differences, using the suggestion of 
Bischoff, relating to the precipitation of the organic substances from 
water in the first instance. Thus I had horizontal cleavage and 
planes of greatest change readily afforded me ; and to increase the 
differences so started and so directed, I had only to suppose that 
the rates of absorption for that part most decomposed, and that 
part least so, are unequal. 
