Vol. 67.] THE LLANDOVERY ROCKS OF MONTGOMERYSHIRE. 421 



yards from the tiny village of Cloddiau. There is no direct 

 evidence here, either of overlap or of unconformity : these will 

 become evident when we trace the group into other parts of the area 

 mapped. Just east of the road the conglomerate is cut off sharply 

 by a small fault, but it comes in again on the south. The con- 

 glomerate is followed by red sandstones and flags, which in turn 

 give place to mudstones. 



Cloddiau Group. — These beds, which are soft pale-grey mud- 

 stones, breaking readily with an uneven splintery fracture, are well 

 seen on the right-hand side of the road, passing to the north-west 

 through Cioddiau. They are over 200 feet thick. 



W en lock Shales. — As we pass along the stream towards Ty- 

 brith Farm, a second gap in the succession is seen to occur ; but 

 immediately under the farm are blue flaggy beds of Wenlock age. 

 Farther up the southern branch of the stream, the beds contain big 

 limestone-boulders yielding "Wenlock or Upper Llandovery fossils. 



Yr A lit Group. — If we follow the branch which runs westwards 

 in the direction of Trefnant, we see that the blue flaggy beds soon 

 give place to a great series of thin buff-coloured shales, which 

 become more sandy and flaggy as we proceed towards Trefnant 

 Farm. 



It will be observed that in this succession there are two gaps. The 

 first is due to overlap by the Powis-Castle Conglomerate, and the 

 other to drift in the stream-bed at Cloddiau. The latter gap can 

 be filled in by examining the lane-section at Cloddiau ; but the 

 apparent conformity of the conglomerate to the beds below is mis- 

 leading, and it will be necessary to consider briefly a second 

 section. 



Confirmatory Section in Gwern-y-brain. 

 (Section II, fig. 2, p. 422.) 



Starting from Sarn Bridge, about half a mile to the north of 

 Guilsfield, a road rnns off to the left up a long narrow valley known 

 as Gwern-y-brain, which cuts through the Gaerfawr ridge. 



Trilobite-Dingle Shales. — These beds are not well exposed 

 in Gwern-y-brain, being obscured by drift. Their relation to the 

 overlying rocks is, however, well shown in the next dingle to the 

 north by Middle House. 



Pwll-y-glo Group. — The peculiar splintery shales and flags of 

 the group are readily recognized in the first exposure in this dingle. 

 Their thickness corresponds pretty closely with that observed in the 

 Moel-y-garth section. 



Gaerfawr Grits. — A great series of massive grits with slialy 

 partings towards the base is now exposed. In places these beds are 



