HARDWICKE'S SCIENCE-GOSSIP. 



169 



THE GEOLOGY OF SHEFFIELD. 



By T. V. HOLMES, F.G.S., H.M.'s Geological Survey. 



HEFFIELD is se- 

 lected this year as 

 the meeting- place 

 of the British 

 Association, and 

 as geological 

 excursions always 

 form one of the 

 pleasantest parts 

 of the Associa- 

 tion's programme 

 to the majority of 

 members, the fol- 

 lowing notes on 

 the geology of 

 the district may 

 possibly be of 

 service. 



It is true that 

 the recently-pub- 

 lished Memoir of 

 the Geological Survey on the Yorkshire coalfield 

 leaves little to be desired by the mining engineer or 

 colliery proprietor, to whom full and accurate informa- 

 tion on all points connected with the coalfield is the 

 one thing needed. But its size and price must ever 

 deter persons simply desirous of making the most of 

 their week at Sheffield with the British Association 

 from attempting to acquire information from such a 

 source. In addition, the geology of the Ordnance 

 quarter sheet (82 N.W.) in which Sheffield stands, is 

 not explained in a brief memoir of thirty or forty 

 pages, on account of the Derbyshire part of it not 

 having yet been mapped by the Ordnance Survey on 

 the scale of six inches to a mile. 



A glance at a general geological map of England 

 and Wales, such as that of Professor Ramsay, shows 

 Sheffield standing not far from the centre of the great 

 Yorkshire and Derbyshire coalfield. This coalfield, 

 measured along a line ranging north and south from a 

 point about ten miles west of Nottingham to the eastern 

 suburbs of Leeds, is about sixty-five miles in length. 

 Its breadth at the northern end, immediately south of 

 No. 176. 



Leeds and Bradford, is twenty-one or twenty-two 

 miles. It gradually narrows southward, being at 

 Sheffield about thirteen miles wide (due east and west), 

 and varying in Derbyshire from seven to ten miles. 

 On its eastern margin it is overlaid unconformably by 

 the magnesian limestone (Permian). On the west the 

 coal measures rest on the series of thick coarse sand- 

 stone with interbedded shales, and occasionally a 

 thin coal, known collectively as millstone grit. 

 This millstone grit forms the high bare moorland 

 which, from the Peak of Derbyshire northward, divides 

 the coalfields of Yorkshire and Lancashire. South of 

 the Peak the underlying Yoredale beds and carboni- 

 ferous limestone are exposed, but too far from 

 Sheffield to come within the scope of this paper. The 

 five great sandstones of the millstone grit here- 

 abouts are : the first (or highest) grit, or rough 

 rock ; the second, third, fourth, and fifth grits ; the 

 two last being also called the upper and lower 

 Kinderscout grits. The coal measures are divided 

 into the lower coal measures, or beds below the 

 Silkstone coal, and the middle coal measures, which 

 include almost all the coals of any importance. In 

 addition may be mentioned the only rocks classed as 

 upper coal measures, the red beds with coal plants 

 seen at Conisborough Pottery. Most of the upper 

 coal measures were removed from the coalfield by 

 denudation, previous to the unconformable deposition 

 of the magnesian limestone above the carboniferous 

 strata. 



The lower coal measures are more remarkable for 

 massive sandstones forming well-marked escarpments 

 than for coals. Few of the coals are of more than 

 local importance. The Ganister and Whinmoor coals 

 are the only ones of this series worthy of notice about 

 Sheffield. In the middle coal measures the Silkstone 

 coal, the lowest of the important beds, is perhaps 

 the first in point of reputation, the Barnsley coal 

 being held in little less esteem. Other coals exist, 

 between these two and above the Barnsley, of fair 

 thickness and quality, but they are not worked in 

 this locality, from their inability to compete with the 

 Silkstone and Barnsley seams, which have no rivals 



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