392 MackiJitosh — O^i the Clifs and Valleys of Wales. 



Gorges and Open Areas not simultaneously Denuded. — The more the 

 forms of the hollows of Central Wales become imprinted on the 

 memory, the more one is led to the conclusion that the longitudinal 

 vales and transverse gorges were not excavated at the same time. 

 The vales and surrounding slopes, with the exception of occasional 

 rocky projections and cliffs, are either level, gently undulating, or 

 smooth and continuous in their outline. The gorges commence 

 most unexpectedly on the sloping side of a ridge, and run right 

 through, with steep, rough, and bare rocky cliffs. (See Plate XV. 

 Fig. 6, which represents the commencement of a gorge to the south of 

 Ehayader.) That rivers often flow through them, and not longitu- 

 dinally along the open country, does not necessarily imply that they 

 were excavated by rivers. These gorges would naturally become 

 deeper and more cleared of gravel than the open area, supposing 

 them to have been formed along the course of a previous slight 

 depression, by a swift oceanic current, as the land was rising ; and 

 rivers would afterwards find their way more easily through them 

 than along the adjacent drift-encumbered vales. ^ I can at present 

 see no theory so little beset with objections as that which would 

 regard these gorges as deep sea-straits formed after the general out- 

 line was given to the neighbouring country ; and this view is con- 

 firmed by the fact, that on the sides of some of these gorges the 

 rocks appear to be sea- worn rather than river-worn. It is likewise 

 favoured by the fact that river-drifts, or traces of river-drifts, sud- 

 denly teiminate at a small elevation above the present river channel, 

 as may be observed in the neighbourhood of Ehayader.* With 

 regard to the excavation of the plain on which Ehayader stands, 

 there are proofs of sea-action on the rocks beneath the drift deposits, 

 consisting of grooves, hollows, and smoothed projections, which are 

 distinct in form from those now observable in the bed of the 

 neighbouring river,^ and equally distinct from ice marks. 



Cwms and Beep Basins near Bhayader. — In the neighbourhood of 

 Ehayader there are phenomena adjacent to, or associated with, the 

 above gorges, which show that the power to which the gorges owe 

 their present form, was sufficient to effect the greater part of their 

 excavation. I allude to the cwms and deep rocky basins, which no 

 river-action or glacial-action will explain. Towards the left of the 

 area represented by Plate XV. Eig. 7, there is a shallow valley 

 descending from the table-land, which, in all probability, was at one 

 time uniformly continuou.s with the valley in the foreground. 

 Superimposed on this valley, and apparently formed at a later 

 period, there is a remarkable cwm, with Grwyn-llyn'' at its bottom, 

 which must have been scooped out by an agent assailing the land 

 backwards. This cwm is identical in form with many hollows on 



^ It is a remarkable fact, that narrow gorges are generally very free from accumu- 

 lations of drift. 



2 The best example of this may be seen about two miles to the north of Ehayader, 

 on the left hand side, near to where the railway crosses the "Wye. 



3 Mr. Randall, F.G.S., tells me there are similar marks on the rocks under the 

 marine drift near Coalbrookdale. 



* Sometimes erroneously called Llyn Gwyn. 



