472 Mr. Bowman on the question, Whether there are 



the middle of the valley on both sides. One only near the 

 little stream of the Clettwr and above the road, seemed, when 

 seen from a distance, to have a pretty level top ; but I observed 

 none with steep sides or escarpments, as though they had been 

 eroded or cut down by a current. The road from Pentre Voe- 

 las to Yspytty winds among them, the higher ones being above 

 it to the S.E., the rest inclining towards the valley below. 

 Similar mounds mask the rocky slope on the opposite bank of 

 the Conway as high as half a mile above Yspytty, becoming 

 gradually lower and thinner till they disappear altogether. In 

 a north-west direction they extend from Pentre Voelas to the 

 opening of the valley of the Machno, and may often be seen 

 on both sides the great road in the less precipitous parts of the 

 gorge, though more frequently and more distinctly on the left 

 bank of the river. From partial openings into several of them, 

 I saw they were formed of local drift or gravel from the neigh- 

 bouring dark schistose rocks, without any large boulders. In 

 one of them, near the great road, there was a streaked or 

 bedded character, the layers being formed of pebbles of dif- 

 ferent sizes, as though they had been left by a current which 

 had varied in intensity. It appeared to me that these hills 

 were not composed throughout of this gravelly drift, but that 

 this material only formed a coat or covering upon the previ- 

 ously existing prominences of the lower Silurian schist of the 

 district, sufficiently thick to conceal the rocky nucleus and to 

 give it a smooth rounded outline. Neither could I attribute 

 their shape to any form or modification of lateral moraine ; 

 and I was of opinion, that even should any one contend that 

 they had originated in a glacier, it would be necessary to ad- 

 mit they must have been subsequently modified by water. It 

 is not easy to understand how so large a mass of diluvium 

 could have been accumulated in this particular locality. See- 

 ing that the river Conway, soon after passing through it, has 

 to make its way along a narrow gorge, and that from the pre- 

 cipitous form of the rocks on each side, it must always have 

 flowed in the same channel, I was at first inclined to suppose 

 that some obstruction might have filled this gorge and pound- 

 ed up the river and the detritus it had brought down from the 

 higher lands. But on examination of their relative levels, it 

 appeared that the gravelly hills above the road east of Yspytty 

 were higher than the surface of a lake so dammed up, and 

 consequently they could not have originated from such a cause. 

 It is singular that in no other neighbouring valley of similar 

 character, were there any accumulations of the same material, 

 and further observation will be necessary to explain their 

 origin. 



