540 Frof. W. Keeping — Geology of Aberystwyth. 



subangular stones with the characteristic scratches, which the 

 geologist recognizes as the result of glacier action. Aberystwyth 

 is built upon that deposit, and every valley in the neighbourhood 

 has its abundant share. 



The best exposure of these old glacial formations is about seven 

 miles south of Aberystwyth, where we find a most interesting 

 section. The cliffs here have been eaten away by the sea, and also 

 by small streams from the land, into the most fantastic forms : 

 deep narrow gulleys, down which we may with some difficulty 

 climb, here and there over-arched above or again opening out into 

 a "chine." In the cliffs lie colossal masses, large blocks, stones, 

 and pebbles, imbedded in a matrix of coarse sandy clay, irregularly 

 mixed together, without any such ari-angement as invariably obtains 

 in ordinary water-formed rocks. Neai-ly every stone has its face 

 or all its faces scratched and smoothed. 



All the stones are such as may have come from within a few miles 

 of where they now lie, grit, greywacke, slate, shale, and mudstone, 

 with a few quartz boulders, forming the great porportion. They were 

 brought down and deposited here by local glaciers — rivers of ice, 

 which had their birthplace in the higher hills inland, and stretched 

 out their long ice-arms and ice-sheets in all directions towards the 

 lower ground. 



Many a Welsh valley has a most typical glacial aspect — a broad, 

 open, half-amphitheatre-like head, which formed the " gathering 

 ground " of the glacier where the snows principally collected, and 

 below ail open valley U shaped in section, its sides regular, and 

 every feature rounded. For in this part of its course below the 

 head the snows had become changed into hard blue ice moving 

 slowly and steadily down, either to its end where it was melted 

 in the lower grounds, or to reach the sea where it was broken 

 up and carried away in the form of icebergs. Such ice-streams, 

 grinding their way down the valleys, would allow of no asperities, 

 no sharp features, but all was smoothed and rounded. 



Wherever a side stream, now entering the old glacier-rounded 

 valley, has more recently cut back for itself a deep bed, its angular 

 valley with rough irregular sides form striking contrasts to the 

 glacier-carved surfaces. This is very well seen from the Devil's 

 Bridge road, looking towards Pen-y-ffrwd, where a small stream 

 leaps down the steep valley side facing you ; and every one who 

 walks much into the country around may find every day fresh 

 examples of the two contrasting types of valley. 



Yet more exact tracks of the local glaciers remain in the rounded 

 rock bosses known as " roches moutonnees," and the polishings, 

 scratchings, and groovings still left upon the solid rock. Such 

 traces of glaciers are well seen in many places around Aberystwyth, 

 such as the valley above Eglws Fach, the Ystwyth valley on the 

 Lisburne Mine private road, in the Eheidol valley at Ty Llwydd, 

 by the road- side between Pont Erwyd and Steddfa Gurig, in the 

 mine works, on the side of Plynlimmon above Steddfa Gurig, 

 and in the Domen valley. In all these places polished and striated 



