210 T. M'KENNY HUGHES ON THE SILURIAN 



find the Bala beds in places highly fossiliferous, aa e. g. near Cerrig- 

 oerion, where I found Leptama sericea, L. transversalis, L. scissa ?, 

 StropTiomena depressa, Palcearca, &c. 



On the top of the hill, sticking out through the flat peaty surface 

 soil, runs a ridge of whitish Grit about 50 feet thick, which becomes 

 finer as we follow it west, until it is represented by a set of nodular 

 striped sandy beds. 



The beds below the Grit have the same kind of double cleavage, 

 noticed in some cases near Corwen in beds below the Cor wen 

 Grit. 



The beds above the Grit are pale imperfectly cleaved slates, passing 

 up into the beds mapped as " Pale Slates " by the Survey, which 

 are, in turn, overlain by the Denbigh Flags. 



On the west the same beds might be expected at a short distance 

 below the Pale Slates ; but I have only hastily run over some of the 

 ground between Llanfihangelglynmyfyr and Cerrigydrudion since I 

 made out the Corwen Section ; and though I came upon fragments 

 which I believe should be referred to this rock, I did not find it in 

 place. Mr. Etheridge informs me that he has Pentamerus oblongus 

 recorded from Cerrigydrudion. 



On the east, after crossing the Llandegla and Bryneglwys faults, 

 we come to rather a difficult bit of ground about Cyrnybrain. I 

 will, however, give the results of a very imperfect examination, as it 

 may save time if any one should go over the ground more carefully 

 before I can offer any thing better. 



Following up the stream by Penycae to the south-east, about 

 one third of a mile south-east of Penycae we find some crushed 

 Sandstone in the bed of the stream, but no clear section. If we 

 proceed straight on, climbing the hill on the north-east of the gully, 

 we soon come upon a long line of fragments of white Grit, nowhere 

 seen in place, but, as far as it can be traced, keeping a uniform dis- 

 tance from the Pale Slates, as if they were portions of a rock broken 

 up along its outcrop. It is true that there are also scattered along 

 the hillside many boulders of felspathic rocks from the high moun- 

 tains to the west ; but they do not occur in a line like the fragments 

 of Grit. In this Grit there are a good many fossils, generally in 

 the form of casts, among which I was able to make out Petraia 

 subduplicata, P. crenulata, and Meristella crassa ; and Pentamerus 

 oblongus is recorded by Mr. Salter from Cyrnybrain. 



The character of this rock is like that of Corwen ; the position 

 of the line of fragments relative to the Pale Slates is the same. 



To the E. and E.S.E., however, I was unable to follow it into the 

 ravine near Plasuchaf ; but up that dingle a thick series of fossili- 

 ferous sandy mudstones occur, dipping at a high angle (50° to 70°) 

 to the south. 



In these beds the following fossils occur — Meristella crassa, 

 Orthis sagittifera, Petraia subduplicata, and P. crenulata. 



I would suggest a comparison of these beds with those in the 

 tramway-section at Llansantffraidglynceiriog ; while the beds on the 

 hill about half a mile to the N.W. of Plasuchaf seem to be exactly 



