109 
cannot be traced with any degree of certainty. In such 
districts the best results that can be arrived at must evidently 
be no more than rough approximations, and it is in this 
light that the conclusions I am going to state must be 
considered. 
Actual exploration has made us fairty well acquainted 
with the measui^es of the Yorkshire Coal Field up to a 
seam known as the Shafton, Billingley, Denaby, or 
Nostel Top Coal, which lies some 430 yards above the 
Bamsley Bed. 
The outcrop of this seam from Bolton-on-Dearne to 
Eoyston Station forms the south-western boundary of the 
district under consideration. A line of fault ranging from 
Eoyston Station to Pontefract bounds it on the north-west. 
On the upcast or north-western side of this fault collieries 
are plentiful; on its down-cast side we have no informa- 
tion from actual exploration beyond a few unimportant 
bore-holes. 
On the south the country for some distance within the 
boundaries just laid down is flat and tame, and it is quite 
hopless to attempt to make out anything of the details of its 
geology ; but there are two tracts more elevated and rather 
more strongly featured, one extending from Clayton-in-the- 
Clay towards Brierley, and the other lying around Ackworth 
and Pontefract, which look more promising, and to these the 
geological explorer betakes himself with some little hope 
of meeting with a reward for his trouble. 
The south-eastern portion of the first of these districts 
consists of an elevated plateau reaching from Clayton-in-the- 
Clay to Brierley Common ; this high gi-ound is capped bv a 
mass of thickly bedded, softish, light brown or bufi" sand- 
stone, which I have named the Houghton Common Eock. 
The escarpment of the rock is sufficiently well marked to 
allow of its being traced with a fair degree of accuracy, and 
