1 24 Coal-measures. 



of them from 3 to 6 feet thick, with beds of under- 

 clay, the whole being interstratified with shales and 

 sandstones. The total thickness of these Coal-mea- 

 sures is about 1,000 feet. The adjoining coal-fields of 

 Le Botwood and Shrewsbury are comparatively of minor 

 importance. The North Wales coal-field in all essen- 

 tial geological points resembles that of South Wales, and 

 lies on the Carboniferous Limestone, which is from 800 

 to 1,000 feet thick. South of Wrexham the whole dips 

 east under the Permian rocks, and further north under 

 the New Eed Sandstone. The Denbighshire part con- 

 tains at least 17 beds of coal, most of which are 

 worked, and the Flintshire part at least 12 beds. 

 A small fragment of the same strata occurs in the 

 central part of Anglesey. It is underlaid by the 

 Carboniferous Limestone, and on the south-east is 

 faulted against the Cambrian rocks. Permian strata 

 overlie it, but the smaller faults and a greenstone dyke 

 which affect the coal do not pass through the Permian 

 beds, which lie unconformably over all. 



In the centre of England the basement beds of the 

 South Staffordshire coal-field rest directly on the 

 Wenlock Limestone of the Upper Silurian series. This 

 field, in the northern part, contains 14 beds of coal, 

 (retting closer to each other by degrees in the south, 

 several of these coalesce to form the thick coal, in places 

 40 feet in thickness, with two thin partings. The rocks 

 are pierced by basalts and a white felspathic -looking 

 trap, which has charred the coals at the points of junc- 

 tion, and is undoubtedly connected with the great 

 basaltic mass, called the Eowley Eag, that overlies the 

 Coal-measures. 



The New Eed Sandstone on the east is faulted 

 against the Warwickshire coal-field, and generally over- 



