430 CLAY IRONSTONE OF THE COAL MEASURES. 



shire. They have long been worked in the Taff Valley, where the 

 iron ore occurs in nearly vertical fissures. 



Forest of Dean Iron Ores. The iron ore of the Forest of 

 Dean occurs in the Carboniferous limestone, and locally in the Mill- 

 stone grit. It is brown hematite or limonite, and occurs in irregular 

 cavities in the rock termed Churns. It is sometimes worked 750 feet 

 below the surface. The iron ore deposits are about 100 yards 

 below the coal measures. The ore varies in appearance from a close- 

 grained black to a spongy black ore, or an earthy ore which on 

 exposure becomes red. The richer ore yields 63 per cent, of 

 metallic iron, the poorer ore about 23 per cent. Some other deposits 

 occur in the Pennant sandstone at Frampton Cotterell, near Bristol, 

 and many other localities in Gloucestershire. 



Iron Ores in the Coal Measures. In the coal measures the 

 iron ore is the argillaceous carbonate of iron which occurs in grey, 

 brownish, or black lumps and nodules, and is found in all the coal- 

 bearing districts, though sometimes the quantity is too small for 

 profitable commercial extraction. 



In the Northumberland and Durham district, on the western side 

 of the coal-field at Consett and Tow Law, the ironstone is in close 

 proximity to the coal. The lowest seam is four to six feet thick. 



In the Yorkshire Coal Field the clay ironstone is largely worked 

 in the Bradford district, where some of the best iron in Britain is 

 made. The South Yorkshire ironworks extend from Leeds by 

 Barnsley to Sheffield and Kotherham. The best beds of ironstone 

 intervene between the Barnsley Thick Coal and the Silkstone, ranging 

 through about a thousand feet of the coal measures. The line is 

 traced southward in Derbyshire, from the valley of the Don to the 

 extreme south of the coal measures, but the bands of nodules are 

 more irregular than in Yorkshire. 



In Derbyshire the ironstones occur on the same horizon as in 

 Yorkshire, between the Barnsley coal which is known as the Top 

 Hard, and the Silkstone, called the Black Shale. The bands which 

 contain the ironstone nodules are known as rakes, the more important 

 of which are the cement rake of Alfreton, the pinder park rake of 

 Staveley, the brown rake of Butterley, the black rake, the dogtooth 

 rake at Staveley, the nodule rake, and the black shale rake, and the 

 striped rake. These beds have a total thickness of 1600 feet. The 

 coal and ironstone together are about 400 feet thick. The dogtooth 

 rake at Chesterfield is an important mine, in which some of the beds 

 are made up of the shells of the bivalve genus Anthracosia. In the 

 Lancashire coal-field clay ironstone occurs, but the beds are thin and of 

 little value. 1 



A little ironstone is raised in Nottinghamshire, and in Warwick- 

 shire. Excellent clay ironstone is found in the Bedworth district near 

 Coventry. 



In Shropshire there are many beds of ironstone, distinguished by 

 local names, such as Chance Pennystone, Blackstone, Yellowstone, 

 1 " Iron Ores of Great Britain," Part i., W. W. Smythe, 1856. 



