a i ie 
Theory of the Origin of Coal. 543 
with the fact that large quantities of vegetables are often matted 
together with marine and estuary shells, phenomena indicative of 
drift. Admitting that the floors of the coal or underclay present a 
great uniformity both in the absence of other plants and in the 
almost general occurrence of the Stigmaria, Mr. Williamson allows 
that a plant, found so very generally in such a position, may haye 
grown in estuaries into which the other vegetables were drifted. 
Acknowledging that the drift theory is open to some objections, he 
stated that one of the greatest of these is, in his opinion, the ex- 
tent and uniformity of some of the thin seams of coal. On this point, 
however, I must be permitted to say, that, if admitted, the difficulty 
must be applied to numberless other deposits of all ages, which 
every one knows must haye been accumulated under water. Sub- 
aqueous action of a tranquil nature is, it appears to me, precisely 
the agency by which we can satisfactorily explain the uniformity of 
many thin layers containing vegetables which are extended over 
wide areas, as in the copper grits of Russia before alluded to. By 
what other possible means, for example, can we explain the wide 
extent of the thin copper slate of Germany with its associated fishes 
on the still thinner bone-bed at the base of the Lias? So far then 
from being a phenomenon which invalidates the formation of coal 
under water, it seems to me, that the very fact of a thin and equable 
deposit is an almost impossible condition, if we insist exclusively upon 
the submergence of forests or jungles én situ, in which considerable 
irregularities of outline must in all probability have prevailed. 
On my own part, and that of my fellow-travellers in Russia, I 
have brought before this Society what we consider strong evidences 
against the too general adoption of this favourite theory. We have 
told you that in many instances the Stigmaria ficoides occurs in 
loose and incoherent sands, as well as in shales, and is frequently 
present where no coal is seen; but what we chiefly insist upon is, 
that all the coal-seams of the South of Russia, without exception, 
alternate repeatedly with beds of purely marine origin, In one sec- 
tion of the Donetz coal-field it has been stated, that at least twelve 
beds of marine limestone alternate in ove vertical section with 
thirteen seams of coal and numerous bands of sandstone and shale, 
in which many species of plants, besides Stigmarie, are confusedly 
heaped together. But we need not go to Russia for such examples. 
The whole of the mountain limestone or lower coal series of the north 
of England is charged, though not to so great an extent, with proofs 
of the alternation of marine deposits with coal and its associated 
sandstone and shale. 
The coast of Northumberland, to the north of Alnwick, presents 
evidences of thin seams of coal resting at once on sandstone, and 
intimately connected with limestone full of sea shells. Advancing 
northwards to Berwick, and to beyond the Tweed, purely marine 
strata re-occur, charged with still more carbonaceous matter ; and, 
in the same series on the north-western parts of England, we have 
frequent examples of the persistence of what must be called ex- 
clusively marine conditions. ‘Throughout that vast succession of 
