Vol. 56.] WENLOCK SHALES OE THE WELSH BORDERLAND. 379 



The alteration in the strike of the beds is well seen in the 

 sections along the Rhayader road, in the Wye, and on the Llanafan- 

 fawr road. At the first of these localities the strike is INT. 40° E. ; 

 in the river the beds appear to be striking due north and south, 

 while on the Llanafan-f awr road their trend is N. 15° W. 



(5) Zone of Cyrtogi-aptus rigidus, Tullb. — The fossili- 

 ferous beds which succeed the flagstones are exposed in three 

 places only in this part of the district ; in Dulas Brook, just where 

 it is crossed by the Llandrindod road, in a quarry near Nant 

 Prophwyd, north-west of Cwm-bach, and on the banks of Nant 

 Prophwyd, below the quarry. 



The exposure in Dulas Brook is small, but very fossiliferous. 

 The beds are striking in the same general direction as the stream ; 

 they consist of hard calcareous shales, yielding the graptolite-fauna of 

 Table I, col. I (p. 378). 



The quarry near JNant Prophwyd contains beds of precisely 

 similar lithological character, but they are probably somewhat higher 

 in the series, tbough still belonging to the same zone. The beds 

 strike across Nant Prophwyd at right angles, and the forms 

 enumerated in Table I, col. K, are characteristic. Omphyma, 

 Orthoceras primcevum, and 0. subundulatum also occur. 



Monograptus retroflexus, Tullb., seems to be confined to this 

 zone ; it is quite as characteristic a fossil as the zone-fossil, and in 

 certain localities would seem to be even more abundant. Obser- 

 vation shows that it is commoner in the highest parts of the 

 zone, though usually present throughout; forms of M. Flemingii 

 (Salt.) begin to occur very abundantly at this horizon. 



I have not been able to estimate the thickness of the O.-rigidus 

 zone, as I have not seen the fossiliferous beds anywhere resting 

 directly upon the flags ; nevertheless, I consider that the beds 

 exposed in Dulas Brook are very near the base, since the flagstones 

 seem to occupy the hill south of the stream. I cannot state where 

 the upper limit should be placed ; but, judging from other localities, 

 I think that the beds in the quarry near Nant Prophwyd cannot 

 be very far down in the zone. 



(6) Zone of Cyrtograptus Lundgreni, Tullb. — The 

 lower beds of the succeeding zone are not very fossiliferous in 

 this part of the area ; they are exposed in an old quarry off 

 the Llandrindod road, north-east of Neuadd, and for some little 

 distance along the bank on the east side of the road. The beds 

 consist of alternations of shales and more flaggy beds ; they have 

 yielded a few graptolites (see Table I, col. L, p. 378). A pygidium 

 of Phacops was also found. 



A good exposure of the calcareous shales is seen behind Gaufron 

 TJchaf Farm, and as a drain had recently been made I found an 

 opportunity of examining a considerable quantity of most promising 

 materia], but, unfortunately, could discern no trace of a graptolite or 

 any other organism. Higher shale-beds are exposed in a copse west 



