Yol. 62.] TAKAN^ON SEKIES OP TAKA.NNON. 663 



sufficient extent is shown in the Tarannon River along this line of 

 section to enable us to see that this group is as important as any 

 of the divisions already noticed, and its collective fauna distinct 

 from that of the overlying Gelli Shales. This group is termed the 

 Brynmair Beds, from the village of Llanbrynmair in the valley 

 of the Twymyn, where their relations to the overlying and under- 

 lying strata are well shown. 



The highest horizon at which graptolites were obtained is a few 

 yards below the footbridge already mentioned. Here the beds 

 consist of thin shales and small flags, and yield : — 



Monograptus runcinatus, Lapw. (C). I Monograptus turriculatus. 

 Monograptus densus, Perner (f. 0). | Petalograptus palmeus, var. tenuis (C). 



On the left bank, south of the bridge, in the scree-slopes, which are 

 here of great height, many specimens of M. runcinatus were obtained. 



Below the footbridge the river-valley is somewhat more open, and 

 the high banks have receded some distance on the east side ; but 

 fairly-continuous exposures may be obtained, either in the bed of the 

 river, or along the road running parallel to it. At one locality along 

 this road, north of Allt-Goch Cottage and about 10 yards south of a 

 place where the beds are extremely disturbed, M. runcinatus (C), 

 M. turriculatus (f. C), and M. Halli, Barr. (?), were obtained from a 

 thin flaggy band which had to some extent resisted the cleavage. 



In a small quarry on the left of the road, some yards still farther 

 south, there is a good exposure of compact blue mudstones ; and 

 similar rocks may be seen at other localities lower down the 

 road, the dip in every case appearing to be north-westerly. 



No graptolites were obtained from these Lower Brynmair Beds on 

 the east side of the river ; but on the west, along a road some 200 feet 

 above the river and opposite Ty-bach, there occurs a fairly-rich fauna 

 of graptolites in some finely-banded grey shales, stained on the 

 surface to a dull purplish colour and weathering deeply to an ashen- 

 grey tint. The species which could be identified include : — 



Rastrites Linncsi, Barr. (R). Monograptus nudus (f. 0). 



Monograptus turricidatus (R). Petalograptus palmeus, var. tenuis 

 Monograptus densus? (R). (f. C). 



Monograptus cf. proteus, Barr. (C). Climacograptus sp. 



This is the last locality examined in the Tarannon Valley ; but 

 similar beds continue for a long distance to the south-east. These 

 are, however, so folded, contorted, and cleaved, that the section is 

 comparatively valueless from the strati graphical point of view. 

 Fortunately, the deficiency is compensated for in the western part 

 of the district. 



The fauna of the Brynmair Group, as here determined, consists of 

 eight species, of which three only are found in the overlying Gelli 

 Group. The first species of Rastrites met with in the descending 

 succession occurs in these beds. Perhaps the most characteristic 

 form is Monograptus turriculatus, and the Brynmair Group may, 

 therefore, be fittingly termed the Monograptus-turriculatus 

 Beds. 



a. J. G. S. No. 248. 2 z 



