122 Coal-measures. 



feet thick, and the Coal-measures, according to De la 

 Beche, 2,765 feet. The limestone contains brown 

 haematite iron ore in cavernous holes. There are in the 

 field 23 chief beds of coal. 



The Bristol and Somersetshire coal-field was also 

 originally joined to the South Wales Carboniferous 

 rocks, till separated by denudation. The Carboniferous 

 Limestone series near Bristol, and on the Mendip Hills, 

 is about 2,500 feet thick, containing the usual marine 

 fossils in great variety. The Coal-measures and Mill- 

 stone grit of the Bristol and Somersetshire coal-field lie 

 in a basin, the base of which is formed of this limestone. 

 The Coal-measures are altogether about 7,000 feet 

 thick, and consist of an upper and a lower series, sepa- 

 rated by thick beds of grit, called the Pennant rock, 

 about 2,000 feet in thickness, and which itself holds 

 beds of coal, some of them of value. Altogether they 

 contain about 46 beds of coal, with a total thickness of 

 about 98 feet. A large part of this Carboniferous basin 

 is unconformably covered by New Eed marl and Liassic 

 and Oolitic strata, and here and there portions of the 

 coal-field are exposed by denudation of the New Eed 

 marl between Bristol and the Mendip Hills, where the 

 beds rise rapidly, and a narrow strip of Coal-measures 

 skirts the Mendip limestones, the whole dipping north 

 at high angles. Similar Coal-measures probably under- 

 lie the marshes, and part of the secondary strata south 

 of the Mendip Hills. 



These three coal-basins, South Wales, Dean Forest, 

 and Bristol, once united, have only been separated by 

 denudation similar to that shown at p. 33. In the 

 case of these coal-fields the intervening spaces are anti- 

 clinal, and the basins synclinal curves, and therefore it 

 is not only possible, but probable, that other coal-basins 



