Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/264

210 find the Bala beds in places highly fossiliferous, as e. g. near Cerrigoerion, where I found Leptæna sericea, L. transversalis, L. scissa?, Strophomena depressa, Palæarca, &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 Corwen 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 distance 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 mountains 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 fossiliferous 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