Vol. 62.] IGNEOUS AND SEDIMENTAKY HOCKS OE LLANGYNOG. 227 



with small horny brachiopods and dendroid graptolites, are exposed. 

 The same beds have been cut through by the road from Forest 

 to College, which here crosses the stream ; and this section shows 

 the iron-staining and iridescence that frequently distinguishes 

 these beds. Traces of dendroid graptolites and horny brachiopods 

 were found here, together with Clonograptus sp., as identified by 

 Miss E. M. R. Wood. 



There are other sections near College and about the village of 

 Llangynog, and also at Lambsfcone Farm, in close contiguity to the 

 Lambstone porphyry ; for instance, in a cart-road leading to the 

 fields behind Banc-y-ffynnon highly-micaceous buff shales dip 

 west 10° north at 50° or thereabouts, towards the porphyry which 

 crops out on some rough ground 50 yards farther to the west. 



At Lambstone Farm, in a lane immediately west of a quarry in 

 the porphyry, is a small opening in faulted and disturbed shales ; 

 there has evidently been some amount of movement between the 

 shales and the porphyry, but the actual junction is not well-exposed. 

 Small outcrops and debris of buff shales may be seen in the 

 adjacent fields. 



There are several outcrops of grit within the shale-area just 

 described, but as they do not appear to lie on the horizon of the 

 massive grits of Pen-y-Moelfre and Glog, and are relatively un- 

 important, they will not be further described. They can be seen at 

 Ffordd and Nant-y-gog ; while another forms a low ridge running 

 from Ffald south-westward towards Pen-y-Moelfre. 



(b) The Grits and Conglomerates. 



The main outcrop of grits and conglomerates first appears near 

 Glog-ddu, nearly 2 miles east of Llangynog village. Here an 

 elliptical outcrop of conglomerate forms a conspicuous ridge imme- 

 diately west of the farm. The rock is exposed on a footpath at the 

 eastern end of the ridge, and there are occasional outcrops along 

 the crest ; but the best section is afforded by a large and con- 

 spicuous old quarry on the northern face of the ridge. This is 

 doubtless the quarry described by Murchison {ante, p. 224) as 

 showing the conglomerate passing down into ' felspar-rock.' The 

 only rock now visible is a conglomerate, consisting of well-rounded 

 pebbles of what appears to be rotten rhyolite, with others of fine 

 white quarrzite, vein-quartz, and shale, embedded in a hard 

 felspathic and sandy matrix, olive-green and buff in colour. The 

 rock is devoid of bedding-planes; and such small evidence of 

 bedding as is shown by the arrangement of the different-sized 

 pebbles suggests a dip of about 20° to the north. There is no 

 obvious difference between the beds at the top of the quarry-face 

 and those at the foot. From Murchison's description we can 

 only conclude that, at the time of his visit, some lower rock, now 

 hidden, was exposed in the quarry, or that he was mistaken in 

 his identification. 



A quarter of a mile farther north the grits and conglomerates 



