546 P>'of. W. Keeping — Geology of Aberysttvyth. 



wliicli is so characteristic of class (1), there is no gathering ground 

 here for the snows to collect in and form a glacier. Again, the con- 

 tinuity of the solid rock all around decides at once against the theory 

 of a moraine dam. No — in Mid Wales we have a crowd of lakes 

 formed by vertical depressions of the solid rock. Very generally 

 the rock-beds are seen sloping down towards the lake on two or 

 three sides, and on one side there may in some cases have been a 

 break in the continuity of the rock — a slowly-formed local fault. 



We have, however, a good example of an ice-formed lake in 

 Llyn Llygad-y-Rheidol under Plyulimmon. The position of this 

 lake is highly favourable for the denuding action of ice. Snows 

 gathered abundantly upon the heights above, and a glacier certainly 

 did descend into the valley in which the lake now lies ; it is then 

 highly probable that the ice here scooped out a hollow. This may 

 well be, but we have besides an obvious cause for the existence of a 

 lake here in the bank of glacial moraine which is now seen running 

 across the valley at the foot of the lake, and through which the stream 

 has cut for about 25 feet. Llyn Llygad-y-Eheidol is then a good 

 example of our class (2), but it is not unlikel}' that the scooping 

 power of ice (class 1) may have deepened its rock-bed. 



The Beach Pebbles. — We must add a few words about the stones of 

 the Aberystwyth beach. Most of these are, of course, rounded pieces 

 of the grit, greywacke, and shale of the cliffs around, but these are 

 scarcely noticeable to the searcher among the more conspicuous hard 

 pebbles which are so numerous and so various. In a few minutes 

 we may pick up quartzites, conglomerates of various colours, felsites, 

 mostly quartz felsite, several varieties of granite, hornblendic 

 granite, syenite, many species of greenstones, and numerous raeta- 

 morphic rocks. We may also find a chalk flint or perhaps a 

 more valuable " pebble " in the technical sense of that word as 

 used by the lapidaries. The homes of many of these pebbles 

 are not yet known to me ; the flints and agates might have 

 come from the chalk and basalt of co. Antrim in the N.E. of 

 Ireland, and other pebbles might have been picked up along the 

 Carnarvon peninsula and carried southwards by currents, but I have 

 not yet been able to identify any such with certainty. On the other 

 hand, it may be that in the Glacial period, while the snow and ice 

 covered the land, icebergs freighted with rocks from other lands 

 floated down the Irish Sea, and dropped their burdens of foreign 

 stones down to the sea-bottom so as to form a Boulder-clay. Such 

 a deposit, now being denuded by marine currents, might well yield 

 us such a variety of pebbles as we find upon the beach. But we 

 have not yet the materials ready to decide which of these theories is 

 the true account. 



Specimens of the rocks, fossils, etc., above mentioned, may be seen 

 arranged in the Museum of the University College of Wales. 



Note. — It will be observed that these Notes on the Geology of Aberystwyth 

 (originally intended for publication in a local guide-book) are very imperfect. To a 

 great extent this is due to the scanty work that has yet been done in our neighbour- 

 hood, and we hope that very soon many of the points now doubtful — such, for 



