542 Prof. W. Keeping — Qeologij of Aherysticyth. 



retaining' their glacial striee and their subangular contours, as in 

 this Esker, 



As the glaciers retired, the melting of the ice and snows gave rise 

 to exaggerated river action, so that the valleys were swept by rapid 

 water-currents, often carrying loads of stones stolen from the 

 glaciers and their moraines. These materials, being rounded as they 

 rolled along the bed of the stream, were roughly arranged and 

 deposited above the proper glacial formations, over which we now 

 usually find them. Such formations are well seen in the cliffs some 

 few miles south of Aberystwyth, and at Clarach; also the coarse 

 pebbly deposits at Tregaron, through which the river has cut, and 

 perhaps some others of our river deposits belong to this stage. 



We have not yet found in our neighbourhood any evidence of 

 such a succession of glacial periods, interglacial periods and great 

 quaternary submergences as are described in other areas. All the 

 phenomena we observe here may well have been produced during a 

 late period by local glaciers. 



We have as yet no means of telling the absolute date in years at 

 which our islands were subjected to these glacial conditions, but we 

 have a very marked record of that date, if we could but read it, in 

 the gorges which streams and waterfalls have cut since the glaciers 

 disappeared. For we have seen that the glaciers left their banks 

 all smoothed and rounded, and it is most conspicuous how far the 

 more rugged and angular beds which have been since produced by 

 the streams of water extend back beyond them. Here then is 

 our record, and when we can determine the rate at which the streams 

 cut back their beds, then we shall easily calculate how long it is 

 since glacial conditions existed here. 



The Latest Geological Phenomena. — Since that time comparatively 

 little geological deposit has been added to the country. The rivers 

 have formed flat lands of pebble beds, loam, and sand, and have 

 again cut down deeply through them, as is well seen in the Eheidol 

 Valley near Ty Llwydd : but these deposits contain no fossils except 

 here and there a piece of wood. Their pebbles are to a great 

 extent derived from the denudation of the glacial deposits, — most 

 barren records. 



In many places however where quiet or stagnant water was kept 

 in, extensive beds of clay and joeat have been formed, the peat 

 uppermost. The Tregaron Valley is a good example of this, for here 

 a very pure and homogeneous soft blue clay is found together 

 with the overlying peat well developed. Very generally such 

 deposits yield many interesting fossils, — shells in the clay and bones 

 of mammals in the peat, but that is not the case here. I have only 

 met with two antlers of the Red Deer (Cervus elaphus) in the clay 

 near Borth,^ and have not found any animal-remains in the peat. 

 This is the more strange, because we know that many animals have 

 lived in this region during the more recent periods, whose remains 

 one would expect to find ; such, for instance, as the Beaver, whose 



^ One of these was presented to the University College Museum by Mrs. Dayies 

 of Antaran. 



