L. Richardson — Glacial Features near Builth Wells. 491 



obviously connected with Glacial action, were observed which appear 

 worthy of record. 



Aberedw is situated near the mouth of a lateral valley of the "Wye 

 (Text-fig. 1). The Wye here pursues an approximately north and 

 south course through a deeply excavated valley in Wenlock, Ludlow, 

 and, further south, Old Ked Sandstone rocks. Viewed from the 

 commanding height of the Carneddau it appears very similar to the 

 Chalford Valley, Stroud. At Aberedw it unites with the Aberedw 

 Valley, which joins it almost at right angles. In pre-Glacial times 

 the Wye flowed through this gorge, and then, as now, was joined at 

 Aberedw by the Edw River ; but instead of the subsequent Edw 

 affecting its junction with the consequent Wye by way of the deep- 

 cleft cut to the south of the bailey-castle-crowned tump south-west 

 of the church (see Plate XXIX), it doubtless flowed Wyewards to 

 the north. In other words, I think that this deep gorge of the Edw 

 has been cut by the Edw River since Glacial times, that the valley 

 to the north of the crag referred to was its pre-Glacial channel, and 

 that this to the south is its post-Glacial one. 



This change of channel was probably due to the ice that occupied 

 the Wye Valley depositing debris from its lateral moraine across the 

 mouth of the Aberedw Valley. To this heap was added terminal 

 moraine matter from the Edw Glacier. While the ice was moving, 

 the terminal moraine matter from the Edw Glacier would combine 

 with that of the lateral moraine of the Wye, and trail southwards 

 as the left-bank lateral moraine of that glacier. But a time would 

 come when the southward movement of the ice would no longer 

 continue, and Wye lateral moraine matter, jy/?« the terminal moraine 

 debris of the Edw Glacier, would accumulate in the mouth of the 

 Aberedw Valley. As the rigorous climate of the Glacial Epoch 

 ameliorated the ice thawed, and the moraine-blocked Aberedw Valley 

 passed into the lake phase. The waters of the lake would become 

 augmented hy the melting. ice and snow of the more elevated tracts, 

 and the moraine dam would be overflowed. Such lakes as a rule evolve 

 an overflow channel between the morainic material and the solid rock 

 bank, and generally, rather naturally, on the downstream side. 



Morainic material must thus be pictured stretching across the mouth 

 of the Aberedw Valley. The water escaping over the southern end 

 of the dam soon commenced cutting into the flaggy rocks of the 

 Silurian, the purely erosive action of the swift-flowing water being 

 accelerated by the filing action of the torrent-driven stones. 



When the Glacial Epoch closed, a passage having been established, 

 the River Edw did not attempt to revert to its pre-Glacial channel, 

 but persisted in its cleft-like gorge and soon graded with the Wye. 



Differential denudation has. now lowered that part of the mouth of 

 the Aberedw Valle}^ where the morainic matter occurs more than the 

 crags along the right bank of the present Edw Gorge (Plate XXIX). 



Standing on the summit of the old bailey-castle and looking down 

 into the deep Edw Gorge, with its rocky banks and swift-flowing 

 river, one cannot restrain feelings of admiration at this excellent 

 illustration of how much work has been accomplished since the 

 rigorous Glacial conditions drew to a close in these parts. 



