GEOLOGY 



removed the upper carboniferous rocks from the central portions of 

 Derbyshire and Yorkshire, and thus separated the coalfields on the two 

 sides of the Pennine Chain one from the other. The Yorkshire, Notting- 

 hamshire and Derbyshire coalfield was considered by Professor Ramsay 

 to lie in the form of a basin, the northern, southern and eastern edges 

 of which lie underneath the New Red, Permian and other overlying 

 secondary strata. He estimated the area of available Coal Measures 

 under these strata to be approximately equal to the area of the coal- 

 field exposed at the surface. 



The depth at which the coal is worked varies considerably. Some 

 shafts are sunk through the Magnesian Limestone which lies unconform- 

 ably on the Coal Measures. Under Bolsover the depth to the ' top hard ' 

 coal is 900 to 950 feet, at Pleasley colliery near Mansfield it was 

 reached at 1,545 feet. 



In Derbyshire the Coal Measures may be divided into the middle 

 coal measures, which are about 2,300 feet in thickness, and the lower 

 or gannister series, which is about 1,000 feet in thickness. The middle 

 coal measures consist of sandstones, shales and clays with ironstones and 

 coal seams. The gannister series consists of flagstones and shales with 

 thin coal seams, under which are floors or beds of gannister. The seams 

 of coal vary from 2 to 7 feet in thickness. 



According to the horizontal section of the Geological Survey the 

 succession of strata from Kirby Woodhouse, through Alfreton Common 

 and Wingfield Manor to Crich are as follows in descending order : 



Permian Rocks 



Marls and Sandstone . 

 Magnesian Limestone (lower) 

 Marls and Sandstone . 



ft. 

 40 

 60 

 3 



Middle Coal Measures 



Strata to Top Hard Coal, about 



Waterloo 



Ell 



Lower Hard 



Furnace 



Black Shale or Clod . . . 



Kilburn 



Shales with Ironstone 



700 



1,600 



Lower Coal or Gannister Series 



Flagstones of Wingfield Manor 

 Shales and Flaggy Sandstones, 

 with two coals underlaid by 

 Gannister floors .... 



Near the southern extremity of the coalfield at Cinderhill colliery 

 the depth to the top hard coal was 655 feet, to the deep hard coal 1,183 

 feet, and to the Kilburn coal 1,995 ^ eet - The principal coals in Derby- 

 shire are the ' top hard ' and ' lower hard ' seams, which produce the 

 glossy coal with long fracture known as splint ; and the ' upper soft ' and 

 ' lower soft ' coals. Different seams have different qualities, and are 

 suited for household, steam or gas purposes. The coal output of Derby- 



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