THE GEOLOGY OF THE DISTRICT 49 



The outstanding problem of the Concealed Coalfield is the possible 

 extent of the field eastwards beyond the River Trent. A recent boring 

 at Harby, within six miles of Lincoln, points to the probability of avail- 

 able reserves of coal in Lincolnshire and in some measure confirms the 

 optimistic findings of the Royal Commission of 1905. Borings to the 

 south of the present field and the out-cropping of Millstone Grits at 

 Castle Donington and Carboniferous Limestone in the TicknaU and 

 Breedon inliers show that there is little possibility of any considerable 

 extension in a southerly direction. The present tendency towards co- 

 operation amongst mining enterprises in the Concealed Coalfield is lead- 

 ing to the more rapid solution of many minor structural problems within 

 the field and though the Geological Survey Memoir on the Concealed 

 Coalfield of Nottinghamshire and Yorkshire (G. V. Wilson, 1926), is still 

 in substance correct, new developments in mining and fuel research have 

 added to our knowledge of the field within the past decade. The Mans- 

 field Marine Band at some distance above the Top Hard seam has proved 

 the most valuable index horizon in the Concealed Coalfield and in the 

 wider correlation of coalfield with coalfield since a corresponding datum 

 has been recognised in Skipsey's Marine Band of Scotland and in the Cefn 

 Coed Marine Band of South Wales. 



The Non-Marine Lamellibranch fauna has proved amenable to zonal 

 divisions and in the productive measures of Nottinghamshire and Derby- 

 shire a definite zonal sequence has been determined. 



The lower limit of the Similis-Pulchra zone is immediately below the 

 Top Hard seam and that of the Modiolaris zone has been fixed with some 

 precision below the Deep Hard group of seams. The Low Main is the 

 highest seam of the Ovalis zone, which zone extends downwards to the 

 horizon of the Kilbum seam which is, in effect, the base of the productive 

 measures of this field. The equivalence of the Kilburn seam of Derby- 

 shire and the Arley seam of Lancashire has now been recognised (Wray, 

 1936) and the Lenisulcata zone extends downwards into the Millstone 

 Grits. 



The upper Umit of the Simihs-Pulchra zone and an attenuated Phillipsii 

 zone are known only in borings and shaft sections in the Concealed 

 Coalfield, where the red unproductive measures of the upper zone are 

 found in an area south of the Mansfield-Newark line, which direction 

 marks the Charnian trend of the Brimmington Anticline under the Permo- 

 Trassic cover. 



It is one problem to speculate on the probable extent of the Concealed 

 Coalfield and another to sink shafts through the water-bearing sandstones 

 of the overlying strata but that is a problem for the mining engineer 

 rather than for the geologist. The application of a cementation process 

 during sinking has been successful in recent enterprises. The effects of 

 mining subsidence on the water undertakings on the overlying sandstone 

 are being watched with some anxiety by water engineers and the city of 

 Nottingham is fortunate in having a reserve supply from the Derwent 

 Valley Scheme. 



S.G.C. 



D 



