500 MJR. 0. T. JOXES OX THE HABTFELL-VALENTIAN [Nov. 1909,. 



blue flags which pass gradually downwards into smooth shales 

 (F. 36) with a profusion of graptolites, mainly of the following 

 species : — Eastrites hybridus (c), Monograptus convolutus var. (v.c.j, 

 M. decipiens, M. lobiferus, M. regularis, Petalograptus sp., and 

 Climacograptus hughesi (v.c). This fauna indicates a high horizon 

 in the pale mudstone-group ; and, from the abundance of a charac- 

 teristic variety of Monograptus convolutus and of Eastrites hybridus, 

 it may be correlated with the band containing Ceplmlograptus 

 cometa in the Nant Fuches-wen section, and with a remarkable 

 band in the Fagwr-fawr quarry described below. The horizon of 

 the last-mentioued band is, therefore, fixed with some certainty at 

 about 20 feet below the Monograptus tenuis horizon. 



This shale-band is separated, by about 18 feet of greenish-blue 

 flags with sandy seams, from a band of rusty shales which were too 

 much cleaved to yield recognizable fossils. Some distance down the 

 slope is a small exposure of ferruginous black shales : they yielded 

 the following species indicative of the leptotheca band : — Mono- 

 graptus cygneus, M. gregarius (?), M. leptotheca, M. cf . millipedia, 

 M. cf . triangularis, Mesograptus magnus (?), Climacograptus hughesi,. 

 and CI. tbrnquisti. 



The band in the quarry with M. convolutus var. was not recognized 

 with certainty in the ravine-section, although it is probably the one 

 that occurs in the centre of the blue flags (No. 9). Its fauna is 

 so characteristic, that it may well be separated off from the lower 

 part of the blue mudstone group which contains the typical form of 

 Monograptus convolutus. It may be called the zone of Ceplialo- 

 graptus cometa, since that fossil has been frequently found in 

 this band, and at no other horizon in the district. 



Near Fagwr-fawr Farm, about half a mile north-east of Kant 

 Meirch, the Castell Fault is seen in section in a ravine, and thence 

 it strikes obliquely up the steep hillside, where its course can be 

 traced by projecting bosses of fault-rock and vein-quartz. About 

 half a mile north-east of the farm is a discarded quarry in thickly- 

 bedded blue flags, intercalated with which are two shaly graptolitic 

 bands. The beds strike due north with a vertical dip, and a total 

 thickness of about 75 feet is exposed in the quarry itself and in an 

 entrance to it cut through the solid rock on its west side. The 

 complete section is tabulated here, for the sake of comparison with 

 those of Nant Meirch and Nant Fuches-wen : — 



Thickness in feet* 

 (6) Ironstained shales ; only debris seen. 

 (5) Blue compact flags, passing up into pale greenish flags, 



about 25- 



(4) Flaggy smooth graptolitic shales, passing down into very 

 soft black shales weathering in pale yellow colours, 



about 5 



(3) Blue and greenish flags striped with sandy seams ; these 



were worked in the quarry 24 



(2) Blue, fissile, ferruginous, graptolitic shales weathering 



ashen white, about o 



(1) Blue flags with irregular gritty bands, seen to about 18 



