ORIGIN AND AGE OF THE SUNS HEAT. 271 



of which geologists arc enabled to measure the thick- 

 ness of strata which may have been removed in places 

 off the present surface of the country, into the details 

 of which I need not here enter. But I may give a few 

 examples of the enormous extent to which the country, 

 in some places, has been found to have been lowered 

 by denudation. 



Prof. Geikie has shown* that the Pentlands must at 

 one time have been covered with upwards of a mile in 

 thickness of Carboniferous rocks which have all been 

 removed by denudation. 



In the Bristol coal-fields, between the River Avon 

 and the Mendips, Prof. Ramsay has shown - )* that about 

 9000 feet of Carboniferous strata have been removed 

 by denudation from the present surface. 



Between Bendrick rock and Garth Hill, South 

 Glamorganshire, a mass of Carboniferous and Old 

 Red Sandstone, of upwards of 9000 feet, has been 

 removed. At the Yale of Towy, Caermarthenshire, 

 about 6000 feet of Silurian and 5000 feet of Old Red 

 Sandstone — in all about 11.000 vertical feet — have 

 been swept away. Between Llandovery and Aberaeron 

 a mass of about 12,000 vertical feet of the Silurian 

 series has been removed by denudation. Between 

 Ebwy and the Forest of Dean, a distance of upwards 

 of 20 miles, a thickness of rock varying from 5000 to 

 10,000 feet has been abstracted. 



Prof. Hull found J on the northern flanks of the 

 Pendle Range, Lancashire, the Permian beds resting 

 on the denuded edges of the Millstone Grit, and these 

 were again observed resting on the Upper Coal- 

 measures south of the Wigan coal-field. Now, from 



* Mem. to Sheet 32, Geol. Survey of Scotland. 



f " Denudation of South Wales/' Memoirs of Geol. Survey, vol. i. 



% " Quart. Journ. Geol. Soc.," vol. xxiv., p. 323. 



