Igneous Rocks. \ 2 7 



district. The lower coal-field of Northumberland, 

 as already stated, is of the age of the Carboniferous 

 Limestone series of Wales, and the Berwickshire coals 

 of Scotland are of the same general age. There is 

 another much smaller coal-field near Ingleton in North 

 Lancashire which contains 8 beds of coal, and in Cum- 

 berland the Whitehaven Coal-measures, which lie on the 

 Carboniferous Limestone, have 14 beds. 



The great Scottish coal-fields lie in a broad syn- 

 clinal curve, in which are the valleys of the Clyde and 

 Forth. Beneath the Calciferous Sandstone and Carbon- 

 iferous Limestone series, Old Eed Sandstone, underlaid 

 by Silurian rocks, rises on the south-east between St. 

 Abb's Head on the east and Grirvan on the west ; while 

 on the north-west the Old Eed Sandstone resting on 

 the Lower Silurian rocks of the Highlands, rises from 

 beneath the same Carboniferous strata between the Frith 

 of Tay and the Clyde, near Dumbarton. The whole tract 

 is about 100 miles in length, by 40 to 50 in breadth. 



The lower Carboniferous strata are much intermin- 

 gled with igneous rock, sometimes felspathic, sometimes 

 augitic. Some of these are intrusive, but large masses 

 consist of truly interbedded lavas, associated with 

 strongly marked and thick strata of volcanic ashes and 

 conglomerates, well seen, for example, on the cliffs 

 between Dunbar and Belhaven. The Carboniferous 

 Limestones, which in occasional bands overlie the Cal- 

 ciferous Sandstone, do not lie in a mass at the base of 

 the Coal-measures, but, as in the North of England, the 

 limestone occurs in several beds, chiefly in the lower 

 part of the series, interstratified with beds of sandstone, 

 shale, and occasionally of coal. In Linlithgowshire 

 and the Campsie Hills limestones are interbedded with 

 trap. Marine, fresh or brackish water, and terrestrial 



