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(iii) The Twymyn below 

 Craig-y-Maes. 



South of the farmsteads of 

 Pennant-isaf and Pennant-uchaf 

 the valley of the Twymyn nar- 

 rows to a deep gorge, and a con- 

 tinuous section is seen in, the bed 

 of the river for fully half a mile, 

 while the crags of Maes and Foel, 

 on either side, afford excellent 

 rock-exposures to the climber. 

 The part occurring between the 

 small footbridge at the extreme 

 northern end and a small tribu- 

 tary stream on the right bank, 

 which has cut a deep and pre- 

 cipitous gorge from the top of 

 Foel down to the main river — 

 a height of nearly 600 feet — 

 lias been examined only in a 

 general way, sufficient to satisfy 

 myself that the sequence, fossils, 

 and structure of the strata 

 in this southern part of the 

 Twymyn Valley correspond with 

 those observed elsewhere. 



The beds here exposed consist 

 of the Llandovery strata and 

 part of the overlying Brynmair 

 Shales, and they are bent into a 

 main anticlinal fold, with nume- 

 rous subsidiary undulations and 

 fractures. As in the other sec- 

 tions already described, there is 

 a normal sequence of rocks on 

 the western limb, while some of 

 the beds are faulted out on the 

 eastern side. 



The Brynmair Beds consist 

 here of pale greenish-grey mud- 

 stones stained with manganese, 

 and hardly distinguishable in 

 mineralogical character from the 

 Upper Dolgau mudstones. At 

 their base a dark shale-band, 

 dipping at 45° north-westward, 

 yields : — 



Monograptus distans ? (C). 

 Monograptus cf. Becki (f. 0). 

 Monograptus Haiti (R). 

 Monograptus regularis (R). 

 Petalograptus palmeus (R). 

 Climacograptus extremus, H .Lapw.(O). 



Judging from the fauna, this band 

 is close to the junction of the 

 Twymyn and Brynmair Groups. 



