268 DISCUSSION'S IN COSMOLOGY. 



now briefly refer to a few of the many facts which 

 might be adduced on this point. 



Evidence from "Faults" — One plain and obvious 

 method of showing the great extent to which the 

 general surface of the country has been lowered by 

 denudation is furnished, as is well known, by the way 

 in which the inequalities of surface produced by faults 

 or dislocations have been effaced. It is quite common 

 to meet with faults where the strata on the one side 

 have been depressed several hundreds — and in some 

 cases thousands — of feet below that on the other, but 

 we seldom find any indications of such on the surface, 

 the inequalities on the surface having been all removed 

 by denudation. But in order to effect this a mass of 

 rock must have been removed equal in thickness to the 

 extent of the dislocation. The following are a few 

 examples of large faults : — 



The great Irwell fault, described by Prof. Hull,* 

 which stretches from the Mersey west of Stockport to 

 the north of Bolton, has a throw of upwards of 3000 

 feet. 



Some remarkable faults have been found by Prof. 

 Ramsay in North Wales. For example, near Snowdon, 

 and about a mile E.S.E. of Beddgelert, there is a fault 

 with a downthrow of 5000 feet ; and in the Berwyn 

 Hills, between Bryn-mawr and Post-gwyn, there is one 

 of 5000 feet. In the Aran Range there is a great 

 fault, designated the Bala fault, with a downthrow of 

 7000 feet. Again, between Aran Mowddwy and Careg 

 Aderyn the displacement of the strata amounts to no 

 less than from 10,000 to 11,000 feet.f Here we have 

 evidence that a mass of rock, varying from 1 mile to 2 

 miles in vertical thickness, must have been denuded in 



* Mem. Geol. Survey of Lancashire, 1862. 



f Mem. Geol. Survey of Great Britain, vol. iii. 



