part 2] PALAEOZOIC eocks of the llangollen district. 183 

 Sequence in the Bryn Beds near Br3^n. 



Thickness in feet. 



6. Blue sandy mudstones with fossils about 70 



5. Subangular conglomerate, or breccia, in parts becoming a 



felspathic ash 2|- 



4. Blue sandy mudstones containing Orthis elegantula 2^ to 3 



3. Coarse felspathic ash, calcareous in part, passing in its 



centre into an agglomerate of compact shale -fragments. 



The top of the ash contains 0. elegantula, and the bottom 



locally is an extremely fine-grained tuff 2^ 



2. Massive felspathic sandstones with abundant fossils locally, 



and some thin bands of shale. (Bryn Sandstone.) 30 



F. Fault, downthrow to the north-east. 



1. Cleaved shales, with thin bands of felspathic sandstone ... 350 to 400 

 Pandy Ash. 



The conglomerate (5) has not been observed in situ elsewhere; 

 but blocks of a rock similar to the agglomerate in 3, built into 

 a wall on the roadside, 200 yards south of Pant (half a mile west 

 of Bryn), were probably quarried near there. 



The lower conglomerate contains pebbles of keratophyric ash, 

 similar to the Pandy Ash, and also pebbles of a curious micaceous 

 and ^&L'^T siliceous rock, which forms part of the Bryn Beds them- 

 selves. It crops out about 470 yards south-east of Pant and also 

 at Ty-nant (on the Oswestry road, half a mile south-east of Brjm). 

 It was here mistaken for an outcrop of the Coed-y-glyn Sill by 

 Grroom & Lake ; microscopic examination, however, shows it to be 

 a clastic rock, very fine-grained in part, but clearly resembling an 

 ash in its coarser portions. 



The presence of these pebbles in the conglomerate at Bryn seems 

 to prove that the rocks near here were sufficiently uplifted during 

 the formation of the Bryn Beds for erosion to reach even the 

 Pandy Ash at the base of the group. Thus it appears that the 

 upward tendency of the Berwyn Dome was in evidence even at 

 that early date. 



(6) Blaen-y-cwm Beds. — These are black graptolitic mud- 

 stones, in which the fossils are poorly preserved. They take their 

 name from a farm near Nantyr, where they are well exposed. 



From their easternmost exposure near G-elli (1| miles south- 

 west of Griyn-Ceiriog) they can be traced as far Avest as the 

 mapping has been undertaken. In this region they overlie the 

 Pen-y-graig Ash wherever it has been proved. The beds disappear 

 east of Grelli. the Dolhir Beds resting directly upon the Bryn Beds 

 (fig. 8, p. 185). _ 



The zonal position of the Blaen-y-cwm Mudstones is still a 

 matter of doubt, on account of the unreliable evidence afforded by 

 the badly-distorted graptolites. Miss G-. L. Elles, to whom the 

 fossils were submitted, thought that the following forms were 

 represented : — Dicellograptiis sp., Dicranograptics tardivscidus 

 Elles & Wood, Di2jloq7^apfi(s (OrtJioqraptvs) caJcaratus Lapworth 

 var. acutus Elles & Wood, D. (O.) caharatiis, var. vulgatiis 



