Vol. 67.] ASSOCIATED EOCKS OF NOETH-EAST MONTGOMEEYSHIEE. 435 



Powis Castle 

 Group. 



x 



X 



X 



X 



List of Llandoveey Fossils [continued] 

 (see pp. 431-35). 



Orthis calligramma, var. davidsoni Lindstr. 



Orthis (Bilobites) biloba Linn 



Orthis bouchardi Dav. ? 



Orth is crispata M'Coy 



Orthis reversa var. mullockiensis Dav 



O. (Herbertella) vespertih'o Sowerby. 



(From underlying beds.) 

 Pentamerus (Barrandella) undatus Sowerb}- 

 Pentamerus (Striclclandinia) lens Sowerby 



Pentamerus oblongus Sow 



Pentamerus cf. Icevis Sow. 



Platystrophia biforata Schlotheim. (From 

 underlying beds.) 



Plectambonites sp 



Phynchonella llandoveriana Davidson 



Phynchonella sp 



Rhynchotreta borealis Scblotheim 



Rhynchotreta cuneata Dalm 



Strophomena pecten Linn 



Strophomena corrugatella Davidson 



Skenidium lewisi Da vid.son ? 



Triplecia insularis Eichwald 



Triplecia cf. nucleus Hall 



Cloddiau & 

 Cefn Beds. 



O 



Cheistiania. 



CO 



00 > 



n 



X X 



X X (base) 



? (base) 

 X 

 X 



On tracing the strata round to Y Frochas, we note that they over- 

 lie the grits there in one or two old quarries where the road crosses 

 the moorland. They consist of thickly-bedded mudstones, which 

 are much cleaved and jointed. A few flags occur, but the whole 

 series seems to be utterly devoid of fossils. In the neighbour- 

 hood of Powis Castle this horizon does not occur at all, being 

 overlapped by the higher Silurian beds. The series can, however, 

 be traced northwards, and yields fossils again in a small quarry at 

 Xlyswen : the strata here are similar to those at Cloddiau, but are 

 not so thick, nor are the higher beds of the sequence exposed. 



(2 6) Cefn Group. — The Pentamerus-Limestone beds at Cefn 

 on the extreme east of the map, seem to represent a higher 

 Llandovery horizon than the limestone associated with the Powis- 

 Castle Group. The beds consist of massive grey calcareous grit, 

 with brecciated limestone-bands and some thin beds of shale. The 

 beds are much broken and contorted by the intrusion of an igneous 

 rock which is similar to that of the Welshpool Dyke, and was 

 formerly seen in the quarry-walls. 



It will be noted that the fossils, on the whole, indicate an 

 horizon nearer to Wenlock age than do those which are connected 

 with the Powis-Castle Beds. It seems, therefore, that the lime- 

 stone facies spread to this side of the valley at a later period than 

 in the areas farther west. 



