90 MR. H. LAPWORTH ON THE [Feb. I9OO, 



the brook resting on the 31. fimbria tus-shales. The latter contain 

 Monograptus fimbriatus, M. communis, M. attenuatus, Diplograptus 

 sinuatus, D. magnus, D. tamariscus, Climacograptus rectangularis, 

 and Orthoceras sp. A small patch of the Nodule Group may also 

 be seen under the Abbey Cwmhir road-bridge on the line of section. 

 A good section of the Rhayader Pale Shales (C) is displayed 

 in the stream some 300 or 400 yards above the road, and again 

 east of Beili-newadd Farm. The rocks do not closely resemble their 

 equivalents at the Tannery. Thin impure grit-bands occur in 

 places, from which Monograptus priodon, Bronn (var.) may be 

 extracted. An examination of the fossils obtained from the same 

 beds in a stream to the eastward still shows that, as in the case 

 of our typical section, the graptolitic faunas of these Pale Shales 

 and the underlying rocks are absolutely distinct. 



(2) Yaynor. 



The most easterly section, which I propose to describe, passes 

 down the narrow valley separating Castle Hill from Llan Goch. 

 This, indeed, is the last section along which any succession may 

 be made out; for, as we extend our examination eastward, the 

 sections are obscured by Drift ; moreover, the divisions which were 

 so distinctly separable in the typical section cannot here be 

 recognized. Again, the rocks are folded and faulted to a considerable 

 extent ; and I do not profess to understand thoroughly the structure 

 of this easternmost area. 



On the line of section itself shaly representatives of the Cerig 

 Gwynion Grits (Aa) occur in theDulas Brook below Great Yaynor 

 Farm, dipping steeply south-eastward (see fig. 5, p. 88). They 

 resemble somewhat the same group as developed on the summit of 

 Castle Hill ; but here the shales and flags predominate. The under- 

 lying Blue-black Shales may be seen in the hedge-banks of the lane 

 leading up to Great Yaynor Farm. A good exposure of the flags of 

 the Zone of Monograptus cyphus (Ac 2 ) has been laid open in 

 the road-cutting east of Cwm Barn. These rocks contain no fossils, 

 but their lithological characters are so well marked that their exact 

 horizon can be assigned to them immediately. On the north side of 

 the farm a few feet of dark brown-weathering, nodular grey flags 

 and shales (Ad^, with small nodules of carbonate of lime, may be 

 observed ; and from certain blue bands in the shales the following 

 fossils have been obtained : — Monograptus communis, M. argutus, 

 Diplograptus sp., Climacograptus rectangularis, and CI. normalis. 



Immediately above this group lies the representative of the 

 Rhayader Pale Shales (C) with Monograptus prio don, etc. At 

 the base is a considerable thickness of arenaceous rock, a few beds 

 of which are crammed with brachiopoda. A description of these 

 shelly bands will be given later (see p. 121). 



Referring to the typical section it will be seen that in the 

 Wye Valley, between the Ddol Shales and the Rhayader Pale 

 Shales, there is a vertical thickness of rock of over 500 feet, and 



