Coal-measures. 125 



laid by the Permian rocks on the west. It contains six 

 beds of workable coal, besides ironstone, and on the 

 south, where the strata pass under the Lower Keuper 

 Sandstones, several of these, as in South Staffordshire, 

 coalesce to form two beds of coal. The lower part of 

 the Coal-measures is traversed by several lines of intru- 

 sive dioritic greenstones running in the line of strike. 



The Ashby-de-la-Zouch coal-field is overlaid by the 

 New Red Sandstone, and partly underlaid by the Car- 

 boniferous Limestone, and partly, probably, by a con- 

 tinuation of the Cambrian rocks of Charnwood Forest. 

 It is divided into two districts or minor basins the 

 eastern, containing 1 5 beds of coal, 1 1 of which are 

 workable ; and the western 1 1 beds. Nine are of superior 

 quality. The Coalbrookdale, South Staffordshire, and 

 Warwickshire coal-fields present so many points of 

 resemblance, that undoubtedly they were all originally 

 formed as one coal-field, and even now in great part 

 may be continuous in the districts that lie between, 

 concealed by Permian and New Red strata. 



North of this coal-field the Carboniferous rocks are 

 somewhat modified in details. Between Derbyshire and 

 Berwick they stretch north and south without a break 

 for 200 miles, by about 60 miles in width. At the 

 southern end, near Derby, the New Red Sandstone over- 

 lies them. West of Cheadle, along the edge of the 

 North Staffordshire coal-field, they are generally faulted 

 against the Permian rocks, north of which lie the coal- 

 fields of Cheshire and Lancashire. The Carboniferous 

 Limestone and Millstone grit rise between these coal- 

 fields, forming the hills of Derbyshire ; and the Coal- 

 measures are thrown off on either side of the anticlinal 

 axis, forming, in the east, the Derbyshire and Yorkshire 

 coal-field, and on the west those of North Staffordshire, 



