48 SCIENTIFIC SURVEY OF NOTTINGHAM AND DISTRICT 



these coals are of little economic importance as such, they frequently 

 prove of value to well sinkers as an indication of the presence of the 

 underlying water-bearing stratum. 



The Rough Rock or First Grit is perhaps the most persistent of the 

 gritstones and as this coarse grained grit is unusually felspathic it appears 

 more prone to disintegrate, on weathering, than other grits in the series. 



Coal Measures 



Considering the long history of the Derbyshire Coalfield the dearth of 

 literature other than publications of the Geological Survey on the Coal 

 Measures is surprising. 



In 1312 coal was being mined at Cossall on the Nottinghamshire and 

 Derbyshire border and locally mined coal probably played a part in 

 driving Queen Eleanor from Nottingham Castle as early as 1257. The 

 local product has long since lived down this unfortunate incident and 

 to-day no two coals are more esteemed than ' Derby Brights ' and 

 Nottingham Ashless '. 



In Derbyshire, where the measures are fully exposed, the mining engin- 

 eer has hitherto been satisfied to depend almost entirely on lithology for 

 purposes of correlation of seams, but in Nottinghamshire where the 

 measures are largely concealed beneath an unconformable cover of 

 Permian and Triassic strata the need for palaeontological indices has 

 been recognised and marine bands and more recently non-marine 

 lamellibranch zones have here proved of value as aids to correlation. 



The productive measures of Derbyshire and Nottinghamshire do not 

 exceed 3,000 feet as compared with 5,000 feet in Yorkshire, and the 

 difl'erence in thickness is accounted for by the relative absence of massive 

 sandstones in the southern portion of the field. Here argillaceous shales 

 and clays predominate and are extensively quarried for bricks and coarse 

 pottery. 



In Derbyshire the lower seams, particularly the Kilburn, Low Main or 

 Furnace, Deep Hard and Deep Soft in ascending order, have been and 

 still are the backbone of the mining industry though thinner seams are 

 now being economically worked. In Nottinghamshire the Top Hard 

 (Barnsley of Yorkshire) and the associated seams in the upper half of 

 the Middle Coal measures are proving even more profitable. 



Whereas the ' Visible Coalfield ' has been exploited for more than 700 

 years and many coUieries are finding it increasingly difficult to maintain 

 an economic output, the working of the ' Concealed Coalfield ' only 

 dates back to 1859, and to-day in Nottinghamshire large collieries with 

 all the advantages of modern equipment and vast resources of accessible 

 coal are capable of an output far in excess of present consumption. 



This inland field has from the first been mainly concerned with the 

 home market and though during the post-war years there has been in- 

 creased competition with other fields which had re-entered the home 

 market on the decline of their export trade, the local field has been 

 fortunate in that new coUieries have been put into successful operation 

 even during the darkest years of the depression. 



