BRITISH ASSOCIATION MEETING. 
437 
the " Memoirs of the Geological Surrey," just issued, the very Unios of these 
beds have a peculiar aspect, differini? much from that of true fresh-water forms. 
They have, he says, a strongly wrinkled epidermis, which is a mark of the 
Myada;, or such burrowing bivalve shells, and not of true Unionidse ; they also 
differ in the interior, as shown by Professor W. King. Seeing that in these cases 
quietly deposited limestones with marine shells (some of them indeed of estuary 
character) rest upon beds of coal, and that in many other cases purely marine 
limestones alternate frequently with layers of vegetable matter and coal, may 
we not be led to modify the theory, founded on the sound observation of Sir 
W. Logan, by which the formation of coal has been rather too exclusively re- 
ferred to terrestrial and freshwater conditions ? May we not rather revert to 
that more expansive doctrine, which I have long supported, that different ope- 
rations of nature have brought about the consolidation and alteration of vege- 
table matter into coal. In other words, that in one tract the coal has been 
formed by the subsidence i/z situ of vast breadths of former jungles and forests; 
in another, by the transport of vegetable materials into marine estuaries ; in a 
third case, as in Russia and Scotland (where purely marine limestones alternate 
with coal), by a succession of oscillations between jungles and the sea ; and, 
lastly, by the extensive growth of large plants in shallow seas. 
The geological map of Edinburghshire, prepared by MM. Howell and Geikie^ 
and recently published, with its lucid explanations, affords indeed the clearest 
proofs of the frequent alternations of beds of purely marine limestone charged 
with Producti and bands of coal, and is in direct analogy with the coal-fields of 
the Donetz, in Southern Russia.* 
In sinking through the extensive coal-tracts around Manchester (at Dukin- 
field), where one of the shafts already exceeds in depth the deepest of the Dur- 
ham mines, rigorous attention will, I hope, be paid to the discovery of the 
fossils which characterize each bed passed through, not merely to bring about a 
correctly matured view of the whole history of these interesting accumula- 
tions, formed when the surface of our planet was first furnished with abundant 
vegetation, but also for the practical advantage of the proprietor and miner, 
who, in certain limited areas, may thus learn where iron-ores and beds of coal 
are most likely to be persistent. In carrying out his survey-work through the 
north-western coal-tracts of Lancashire, to which the large, or six-inch, Ord- 
nance-map has been applied, one of the Secretaries of this Section, Mr. Hull, 
has done good service in accurately defining the tracts wherein the elevated 
coal deposits are covered by drift only, in contradistinction to those which are 
still surmounted by red rocks of Permian and Triassic age. In seeing that 
these are eagerly bought by the public, and in recognising the great use which 
the six-inch survey has proved in the hands of the geological surveyors in 
Scotland, our friends in and around Manchester may be led to insist on having 
that large scale of survey extended to their own important district. By re- 
ferring to the detailed delineations of the outcrops of all the Carboniferous 
strata in the cities of Edinburgh, Haddington, Eife, and Linlithgow, as noted by 
Professor Ramsay and MM. Howell and Geikie, the coal-proprietors of Eng- 
land will doubtless recognise the great value of such determinations. 
Concerning the Permian Rocks, which were formed towards the close of the 
long palaeozoic era, and constitute a natural sequel to the old Carboniferous 
deposits, it is to be hoped that we shall here receive apposite illustrations from 
some of our associates. 
When Professor Sedgwick, thirty-four years ago, gave to geolo^sts his 
excellent Memoir on the Magnesian Limestone of our country, as it ranges 
from Durham, through Yorkshire, into Nottinghamshire, he not only described 
the numerous varieties of mineral structure which that rock exhibits, noting at 
* See Russia in Europe and the Ural Mountains. Vol. I. 
