﻿412 MISS DEBW AND MISS SLATER ON THE [Aug. I9IO> 



This series of tough pale rocks we have grouped together under 

 the name of Pengelli Mudstones. For half a mile there are 

 no exposures, and the rock is next seen in the bank where the road 

 turns sharply down hill through a larch wood to a stream. Here 

 its character is somewhat altered, the mudstones have become more 

 massive, more thickly bedded, and slightly nodular, dull grey in 

 colour, and weather yellow. No fossils were obtained. After a 

 second stream has been crossed, the rocks are well seen in the road- 

 side for 200 yards. Here once more grits come in, and with their 

 appearance begins the rolling, so characteristic of these higher beds. 

 The grits are grey and banded, reaching a maximum thickness of 

 3 inches. The interbedded shales are thin, flaky, dark grey,, 

 weathering to a yellow-brown. The cleavage practically coincides 

 with the dip ; but, despite this advantage, long search failed to 

 reveal any fossils. The dip varies from 70° S. 20° E. to 48° N. 

 20° W. There is no change lithologically for nearly a mile, when a 

 stream is crossed and the road rises. Near Cwm Dawe in the road- 

 side are finely laminated blue-black and grey shales, splitting into 

 fragments of papery thinness, with smooth black surfaces, marked 

 by very noticeable concentric orange weathering ; there is no trace 

 of cleavage. The gritty bands still persist, and the dip still con- 

 tinually changes in direction. These beds furnished one specimen 

 of Monograptus marri. The great distance across the strike, between 

 the two localities yielding this fossil and no other, is easily accounted 

 for by the rolling which sets in among these higher beds. 



Confirmatory Sections. 



(a) Section along Llanybyther Eoad. — The same series 

 of rocks is crossed obliquely by the Llanybyther road, where is 

 obtained confirmatory evidence of the sequence just described: 

 as before, the section is very discontinuous, and fossil localities are 

 even less frequent. 



(Cj). — The first exposure is in the Clynmarch Grits, which are 

 quarried just behind Sunnybank Farm. The character of the rock 

 is absolutely similar to that in the other quarries on the north-east, 

 and the fossils obtained were the same. 



(C 3 ). — There is no further exposure until Cil Wenau is reached, 

 three-quarters of a mile distant ; here a considerable stretch of 

 Pengelli Shales is exposed, with the same characteristics as those 

 that were displayed along the Lampeter road, but for the appear- 

 ance of thin grit bands. Where the road bends sharply north- 

 westwards to Llethr-bledrig, one specimen of Monograptus marri 

 was found in greyish shales, with little cleavage and orange 

 weathering. Immediately north of this a dip of 52° south 20° east 

 was observed, showing that the rolling comes in again, at about 

 the same horizon as before. 



Just beyond Khyd-cymmerau the road divides into two. About 

 600 yards along the northern branch, and on the same line of 



