TRANSACTIONS OF THE SECTIONS. 61 
are twelve in number, giving an ageregate of about 50 feet of coal. The most 
famous of these seams, from above downwards, are the High Main, the Yard Coal, 
the Bensham, Five Quarter, Low Main, Lower Five Quarter, Ruler or Hutton 
Seam, the Townley or Beaumont, the Busty Bank, Three Quarters, and the Brock- 
well. 
On the east the coal-measures are overlain, in a line running from South Shields 
past Houghton-le-Spring to near Bishops Auckland, by the Permian Series, repre- 
sented by the Magnesian Limestone and the Lower Red Sand—that unequal and 
water-bearing bed which forms the great obstacle to the sinking of shafts to the 
underlying coals. Prejudice, it is well known, even after the difference of these 
strata from the mountain limestone was proved, long contended that the coal could 
not be found continuous beneath the magnesian limestone; and it is still asserted 
that the seams have proved inferior when they pass beneath it, as shown especially 
by the failure in certain tracts of the Five Quarter and Hutton Seams. But no 
sufficient reason is apparent why such deterioration is not rather to be ascribed to 
that variation in quality which all seams are found to undergo when followed over 
a large area, than to the evil influence of an unconformable upper formation. The 
variation here alluded to exercises an important bearing on the commercial rela- 
tions of different parts of the field; and whilst the best “household coal,” bright, 
giving a black cinder, and free from ash, extends from the Tyne to the Wear, and 
from the last river to Castle Eden, and occupies another area about Bishops Auck- 
land, the steam coal, more dense, and yielding a white ash, characterizes the dis- 
trict beginning some fiye miles north of the Tyne; and the tender coal, best suited 
for coking, is largely worked all along the line of the western outcrops, from Ryton 
down to the outskirts of Raby Park. 
As regards the physical agencies which have impressed its present form on this 
great coal-field, I would remark that they appear to have acted with upheaval in a 
north and south direction, as evinced by the regular strike over a great length of 
country. This was accompanied or followed by transverse fractures resulting in 
several very pronounced lines of fault. Two of these, running respectively east- 
north-east and east-south-east, are the whin or basaltic dykes named the Hett and 
the Cockfield dykes. Of the others the most noticeable is the great fault called 
the Ninety-fathom Dyke, which, starting from the coast near Cullercoats, where it 
displaces the strata to that amount, ranges past Gosforth to Blaydon, and then 
entering on the more hilly ground, may be traced westward to the New Red Sand- 
stone of the 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 lime- 
stone district, a long strip of the coal-measures of the Newcastle field, and thus to 
give rise to the collieries of Stublick, Midgeholm, Tindal Fell, &c. 
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 direction of the trough- 
ing and folding, and the vast number of thin seams which are so noticeable in the 
latter, we may conclude more properly that it is in the peculiar and often similarly 
circumstanced coal-field of Somersetshire that we have to seek for the direct con- 
tinuation 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 or “ post,” little dif- 
ference of opinion is now entertained. That the coal itself has been formed purely 
from vegetable matter can no longer be questioned. The view originally pro- 
pounded by De Luc, that the vegetation now composing our coal-seams grew on 
the soil which actually forms the bed or “thill” of the seam, has met with very 
general acceptance, notwithstanding the difficulty of adopting it in certain excep- 
tional cases. That this dense mass of vegetation flourished and swelled over an 
area frequently subjected to depression beneath the neighbouring water admits of 
but little doubt. Such an hypothesis serves to explain not only the equable cover- 
ing 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 mollusca and fishes 
which tenanted the waters of those depressions, but indicates also the mode in 
which certain seams have been divided by a parting almost imperceptible in one 
place, but amounting to many feet in another. The well-known Busty Bank seam 
