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ON THE GEOLOGY OF THE CENTRAL PORTION OF THE YORKSHIRE 
COAL FIELD, LYING BETWEEN PONTEFRACT AND BOLTON- 
ON-DEARNE. BY A. H. GREEN, M.A., F.G.S., PROFESSOR 
OF GEOLOGY IN THE YORKSHIRE COLLEGE OF SCIENCE, 
LEEDS, OF H.M. GEOLOGICAL SURVEY. 
The district with which I propose to deal in the present 
paper comprises one of the least known portions of the 
Yorkshire Coal Field. Workings naturally commenced 
along the edges of the basin where the coals lie nearest to 
the surface ; as the shallower portions of the seams became 
exhausted, explorations gradually advanced more and more 
towards the interior of the field, and they now extend over 
an encircling belt of considerable breadth, and have even 
been pushed in some cases, where railways offer facilities of 
carriage, for long distances towards the centre of the field. In 
these explored districts the Officers of the Geological Survey 
have been able, thanks to the liberality of the coal owners in 
communicating information, to frame maps which show in 
considerable detail all the minuter features of the geology. 
But there yet remain tracts, of what the one now before us is 
an instance, where the sum total of our knowledge amounts 
to very little. They are unpierced by a single shaft or bore- 
hole, and unluckily it is very often the case that at the same 
time there are but slight natural facilities for making out 
their geology. They are for the most part flat and low lying, 
and are consequently covered to a great depth with superficial 
rain- wash, and the streams have not fall enough to enable 
them to cut down to the solid rock, so that natural sections 
are few and far between, and poor where they do occur. 
Again the few thick sandstone beds that occur are soft and 
very irregular, and theii* escarpments are hence feeble and 
ill-marked, fitful and liable to die away altogether, and 
