BEITISH ASSOCIATION MEETING AT NEWCASTLE. 367 
tlie neighbourhood of Carlisle. Along this western part of its course its 
throw is so great, as to inlay, as it were, on its north side, in the midst of 
the limestone district, a long strip of the coal-measures of the Newcastle 
field, and thus to give rise to the collieries of Stublick, Midgeholme, Tindal 
Fell, etc. The coals and other strata of this field have sometimes been 
compared with those of Belgium ; but when we regard the decided east 
and west troughing and folding, and the vast number of the seams 
which are so noticeable in the latter, we may conclude more properly that 
it is in the peculiar and often similarly circumstanced coalfield of Somer- 
setshire that we have to seek for the direct continuation of the field of the 
low countries. Let us now cast a brief glance on the theoretical side of 
the subject. Upon the mode of origination of the limestone, the shale, and 
the grit, little difference of opinion is now entertained. That the coal itself 
has been formed purely from vegetable matter can no longer be questioned. 
The view originally propounded by De Luc, that the vegetation now com- 
posing our coal-seams grew on the soil which actuall}^ forms the bed or 
"thill " of the seam, has met with very general acceptance, notwithstand- 
ing the difficulty of adopting it in certain exceptional cases. That this 
dense mass of vegetation swelled over an area frequently subjected to de- 
pression beneath the neighbouring waters admits of but little doubt. Such 
an hypothesis serves to explain not only the equable covering of the coals 
with their roofs of muddy or sandy matter, afterwards consolidated into 
shale and grit, and exhibiting to our gaze the remains of mullusca and 
fishes which tenanted the waters of those depressions, but indicates also 
the mode in which certain scams have been divided by partings almost 
imperceptible in one place, but amounting to many feet in anotlier. The 
well-known Busty Bank seam of the western district, some 5 feet thick, 
including a clay band of 11 inches, is thus divided in a distance of 2 or 3 
miles, by the increase of the parting to 18 feet, into the stone-coal and the 
Five-quarter at Garesfield Colliery. A still more remarkable instance is 
the Tow Law seam at these works, 6 feet 3 inches thick, which, by the in- 
crease of a parting as it goes eastward, exhibits at Bowden Clohc Colliery, 
only 3 miles away, two seams divided by no less than 16 fathoms of ground, 
in which beds of sandstone or pert and their seams of coal have been in- 
tercalated. Such partings, when composed of shale, are often one mass 
of stigmarian impressions, and thus form no exception to the generally 
important part which that fossil plays as tlie root of the chief plant of 
the coal ; but when the partings consist of fine-grained clean sandstone, 
showing no trace of rootlets, I confess that the appearance of bright solid, 
coal resting upon them seems to me to demand some other explanation. In- 
stances of this kind observed in South Staffordshire and in the Whitehaven 
collieries, induce me to think that the material must in some cases have 
been introduced between the laminae, and sometimes even diagonally 
athwart them, subsequently to the solidification of the coaly matter. But 
there are several curious phenomena as to which a doubt frequently arises, 
whether they are due to action during or after the formation of the coal, 
and deductions of no small practical importance sometimes depend on the 
question. Thus Mr. Hurst has given to the Institute a very exact account 
of irregularities, especially s wellies, ornarrow depressions in the Low Main 
coal, which appears to have been formed prior to the deposition of the 
upper seams. On the other hand, Mr. Marcus Scott has excellently de- 
scribed a broad valley of denudation which was eroded in the coals of the 
Shropshire field, and filled in with higher unproductive measures. Again, 
with some of the slips and faults or troubles we may sometimes observe 
both coal and ironstone beds so to change on approaching them, or to vary 
