﻿408 MISS DEEW AND MISS SLATER ON THE [Aug. I^IO, 



The Pen-y-ddinas Grits are only seen to the south-east of 

 Llansawel, where they form the greater part of the abrupt hill 

 dominating the village, and the eastern extremity of Banc Beili 

 Tew. This rock is a very hard grey quartzite, and occurs in 

 massive beds, without interbedded shales. Its character is very 

 uniform throughout the exposures ; and we were unable to find the 

 least trace of fossils. 



The grit is never found in contact with the conglomerate, so 

 that the relation of the one to the other is difficult to establish ; 

 but we believe them to be on much the same horizon, for the upper 

 member of this group, the Llathige Shales and Mudstones (B ), 

 appears to follow directly on both grit and conglomerate. We were 

 however, unfortunate in never obtaining fossils from the shales in 

 the close neighbourhood of either of these coarse deposits, and we 

 had therefore to rely upon the lithology. 



(B ) The Llathige Shales and Mudstones. — The quarry 

 at Cae-gwyn, under the southern slopes of Shon Nicholas, has 

 furnished probably the lowest graptolitic horizon that* we have 

 found in this district. The rock here consists of dark -grey shales, 

 weathering to pale greenish and rusty tints, and thin well- bedded 

 grits, banded and sandy, with the same rusty weathering. The 

 slabs of grit are often characterized by a few large, scattered 

 spherules of pyrite, which weather out brown. Cleavage is here 

 hardly apparent, and the beds dip at 45° N". 10° W. This locality 

 (L. 1 on the map, PI. XXIX) has yielded several specimens of 

 Climacograptus normalis, Lapw., and nothing else. 



The mudstones have been largely quarried on the north-western 

 face of Banc Bwlch Cefn Sarth, and the two most important sections 

 are immediately south of the Pumpsaint-Llandovery-road, a quarry 

 near the farm of Bwlch Cefn Sarth (L. 6), and another close to the 

 farm of Llathige (L. 8). The rock is a compact blue mudstone, 

 and is worked along the cleavage-planes in large massive slabs. 

 The bedding is at a high angle : 70° at Bwlch Cefn Sarth and 90° 

 at Llathige. In the first-mentioned quarry the graptolites are all 

 preserved in pyrite, but are badly crushed by the cleavage; in 

 the other, however, the fossils are much better preserved, and we 

 obtained : — Mesograptus modestus, Lapw., Climacograptus rectangu- 

 laris, M'Coy, and CI. normalis. This assemblage forms a typical 

 modestus-ftag fauna. 



A very similar rock is seen in the large quarry in Caio village ; 

 here the bedding is horizontal, and the cleavage at right angles to 

 the bedding. The fossils obtained indicate the same horizon. 



There are many exposures all around the old Koman levels and 

 gold-mines of Pumpsaint. At two different points we have obtained 

 fossils indicating again the zone of Mesograptus modestus, and 

 probably the whole mass of rock is of much the same age. 



In the northern part, where the workings are still carried on, 

 there is evidence of a great amount of disturbance. The rocks are 

 intensely cleaved, sharply folded into broken anticlines, and riddled 



