68 
ON THE VARIATIONS IN THICKNESS AND CHARACTER OF 
THE SILKSTONE AND BARNSLEY COAL SEAMS IN THE 
SOUTHERN PART OF THE YORKSHIRE COAL-FIELD, AND 
THE PROBABLE MANNER IN WHICH THESE AND SIMILAR 
CHANGES HAVE BEEN PRODUCED. BY A. H. GREEN, 
3LA., F.G.S., PROFESSOR OF GEOLOGY IN THE YORKSHIRE 
COLLEGE OF SCIENCE, LEEDS. (PLATE IV.) 
Oyer tlie soutliGm part of the Yorkshire Coal-field, as far 
north, as the village of Cawthorne, the Silkstone coal main- 
tains, in spite of local variations, a fairly constant character. 
It consists of two beds of coal, each averaging some 2 feet 
6 inches in thickness, separated by a band of dirt. Over a 
very great part of the area where the coal is known, the dirt 
parting is very thin ; here and there, however, it swells out 
to a very considerable thickness, and in one place it even 
reaches a thickness of ten yards. In the neighbourhood of 
Cawthorne a very important change comes over the seam, 
additional dirt partings come in and it breaks up into several 
beds of coal. Following it to the north-west the beds of 
coal decrease in thickness, whilst the dirt partings swell out, 
and there can be little doubt that if it were possible to 
trace the seam still further in this direction, it would be 
found that the coal thins away altogether, and that the seam 
is replaced entirely by stone and shale. On this point, how- 
ever, it is impossible to speak with certainty, for after passing 
Cawthorne the seam becomes so much deteriorated that no 
attempts have been made to work it, and to the north-west 
of that village there is a belt of country some two or three 
miles broad which is totally unexplored. After passing this 
problematical groimd, however, a tract is again reached 
yielding workable seams, and among these there is one known 
as the Blocking coal, which holds a position in the measures 
