206 SCRATCHES NEAR LLANRWST. GRAVEL IN SOUTH WALES. 
EVIDENCE OF DILUVIAL ACTION IN WALES. 
In North Wales Mr. Underwood has noticed a similar effect of 
diluvial scratches and scorings on the surface of the slate-rock, where 
it is immediately covered with a very thick bed of gravel, in a section 
of the new Irish road at Dinas Hill, about one mile east of Bettws y 
coed, near Llanrwst, and about a mile and a half east of the bridge 
called Waterloo Bridge. It is a case completely similar to those I 
have quoted from Sir James Hall, and Colonel Imrie. 
The deposits of gravel I have already mentioned in the Vale of 
Clwydd, and the valleys excavated in the hills adjacent to it, are 
equally of diluvial origin; and the whole low country of South 
Wales, from the estuary of the Severn for several miles inland, is 
strewed over irregularly with large boulders and beds of gravel, 
derivative by diluvial actions from the mountains that flank this 
district on the north*. The surface and sides of these mountains 
are also intersected by very deep and narrow valleys of denudation ; 
a good example of which is afforded by the valleys of the Taff, the 
Ebwy, and the Neath. 
* Near Penllergare, in the parish of Langerelach, about 5 miles north of Swansea, 
Mr. Dillwyn pointed out to me large blocks of mountain limestone, some of them 6 feet 
square, in the midst of gravel, which is chiefly composed of the debris of coal measures. 
The nearest limestone rock on the north of this spot, is at the distance of 10 miles. 
