A HISTORY OF DERBYSHIRE 



shire has increased considerably, and although at present greater than 

 that of Nottinghamshire, Mr. Stokes thinks that it has almost reached 

 its limit and will in turn be exceeded in the neighbouring county. At 

 the commencement of the nineteenth century the coal raised in Derby- 

 shire amounted to about 270,000 tons, whilst during the last year of the 

 century it had reached 1 5^ million tons. 



In addition to the main coalfield there are two others of small area 

 which deserve a brief mention. That in the southern portion of the 

 county is a continuation of the Leicestershire field. The boundary is 

 very irregular. It enters the county near Calke Abbey, runs nearly to 

 Ticknall, and in a zigzag line to Bretby colliery. These Coal Measures 

 dip south until close upon the county boundary, where they are overlain 

 by Triassic rocks. The coal of this district, the principal seam of which 

 is called the main coal, is generally used for manufacturing and steam 

 purposes. 



The north Derbyshire coalfield is a continuation of the Lancashire 

 and Cheshire coal basin. It covers only a small area of the county. Four 

 seams are worked, but no large amount of coal is raised. It is mostly 

 employed for local purposes, and is too inferior in quality and too far 

 from a railway to compete with the coal raised in the east Derbyshire 

 coalfield. 



Clay ironstone is found either in nodules or in beds amongst the 

 Coal Measure shales. It is in the form of a carbonate of iron mixed often 

 with argillaceous and silicious material. Though it was once largely 

 worked in the county its place has now been taken by the North- 

 amptonshire ore, which can be delivered more cheaply at the Derbyshire 

 furnaces. 



The fossils of the Coal Measures are indicative of estuarine or 

 brackish water conditions, with a land flora alternating with layers con- 

 taining marine fossils. The presence of the numerous seams of coal and 

 beds of carbonaceous shale point to the profusion of vegetable growth 

 during that part of the carboniferous period when the Coal Measures 

 were being formed. The flora, consisting of some hundreds of forms, 

 has only distant representatives to-day in the tree ferns of tropical swamps 

 and jungles and the horsetails and club mosses of temperate regions. 

 The seams of coal are composed of compressed and mineralized remains 

 of this vegetation. The vegetable matter becomes decomposed, gives off 

 gases, passes through states similar to those of peat and lignite, and is 

 finally transformed into coal. 



Some coals were undoubtedly formed on dry land or in swampy 

 marshes. That such was the case is shown by the uniformity of 

 character and thickness which a seam of coal often maintains over a 

 considerable area, and by the fact that fossil trees are now found in 

 the Coal Measures in the position in which they grew. A coal seam 

 generally rests on an under-clay or shale or gannister, called ' seat earth ' 

 by the miners. The fossil trees called sigillaria are found erect in the 

 coals with their roots or stigmaria penetrating the under clay. These 



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