(588 
with a dirt parting. The latter, though here and there 
swelling out to a thickness of seven or eight yards, rarely 
exceeds a foot, and is very often only a few inches, in thick- 
ness, anywhere between Sheffield and Silkstone ; the thick- 
ness of workable coal over the same district ranges from 
four feet to five feet six inches. Between Silkstone and 
Cawthorne the parting increases very rapidly in thickness, 
and on the north of the latter village the two beds are 
separated by a mass of shale and stone of eight or nine 
yards, while the coal itself is much reduced in thickness. 
Between Cawthorne and West Clayton is a tract of unproved 
ground, over which some thin coals, perhaps the still further 
attenuated representatives of the Silkstone, have been 
worked to a small extent in bygone times. To the north- 
west of West Clayton, a coal known as the Blocking Bed is 
largely gotten : it holds the same relative position in the 
measures as the Silkstone Coal, of which it must be looked 
upon as in some measure the equivalent. It is of good 
quality, and ranges from eighteen inches to two feet in 
thickness. 
We shall come across changes like those just described in 
the thickness and character of other coal seams, and I hope 
some day to be able to explain to you how they were 
brought about. 
We may now turn to the hundred yards of measures 
between the Silkstone and Park Gate Coals. 
A thick bed of sandstone, known as the Silkstone or 
Sheffield Bock, is often found above the Silkstone Coal : it 
forms a ridge ranging from Dropping Well, through Winco- 
bank Wood, down to Sheffield; and is also well shown at 
Banks Hall, near Cawthorne. Like all the Coal-measure 
sandstones, however, it very frequently dies away altogether, 
and is replaced by shale. 
About ten or fifteen yards above the Silkstone Coal is the 
