$22 Rivers of Wales. 



length of that beautiful valley, through various Per- 

 mian rocks, for nearly forty miles. At the mouth of 

 the valley, at and near Carlisle, a patch of New Eed 

 Marl lies on the Permian sandstones, and on the Marl 

 rests the Lias. Whether the whole length of the Per- 

 mian strata of the Vale of Eden was once covered by 

 these rocks it is impossible to determine, but I believe 

 that it must have been so to a great extent, and also 

 that the Lias may have been covered by Oolitic strata. 

 A great fault east of the Eden has thrown these forma- 

 tions down on the west, so that the faulted edge of the 

 Permian beds now abuts on the high Carboniferous 

 hills that form the eastern side of the valley. As these 

 Permian and Secondary were denuded away by time, 

 the present river Eden began to establish itself, and 

 now runs through rocks in a faulted hollow, in the 

 manner shown in fig. 104. What is the precise geological 

 date of the origin of this great valley and its river 

 course in their present form, I am unable to say ; but 

 I believe that it may approximately be of the same age 

 as the valleys last described : that is to say, of later date 

 than the Oolites, and probably it is later than the Creta- 

 ceous and Eocene, or even than the Miocene epoch. And 

 so with the other rivers of the west of England the 

 Lune, the Eibble, the Mersey, and the Weaver. 



In Wales, the Dyfi partly runs in a valley formed 

 by denudation along an old line of fault ; and the Teifi 

 in Cardiganshire, and the Towey in Caermarthenshire, 

 in parts of their courses along lines running in the 

 direction of the strike of soft Llandeilo flags, sometimes 

 slaty and easily worn down by water, their valleys being 

 bounded on either side by hills to a great extent formed 

 of harder Silurian grits. 



To sum up the subject: It seems to me that all 



