156 ME. P. R. COWPER EEED ON THE GEOLOGY OF [May 1 89 5, 



Llandeilo lavas and ashes, which extends right across the country to 

 Newport and the river Clydach. Near Newport the horizon and 

 succession of the overlying beds is fortunately determinable, so that 

 the age of this great volcanic belt can be definitely fixed. The beds 

 immediately resting on the lavas are grey tuffs, and these are suc- 

 ceeded by tough calcareous slates, on which rest 150 feet or more 

 of dark graptolitic shales. The grey tuffs may reach 50 feet in 

 thickness, as near the 'Rising Sun' Inn on the road from Newport 

 to Cilgwyn. They are found again about i mile south of New- 

 port, near Fountain Hill Farm, and also in ' Old Quarries,' about 

 100 yards south of Pen y Feidr farm, south-west of Newport. At 

 several other localities along their strike, which is nearly due east 

 and west, they are exposed. 



The tough slaty beds above them do not attain a thickness of 

 more than 20 feet, and thin calcareous bands occur among them. The 

 only fossils that have been found in them are Siphonotreta micida 

 and a cyprid. The brachiopod is very characteristic of the beds 

 with Ogygia BucM at Pen Cerrig, Builth, in the typical Upper 

 Llandeilo. 



The graptolitic dark shales, 150 feet or more in thickness, occur 

 above these slaty beds, and are well exposed in the lane from the 

 Castle, Newport, to Fern Hill Cottage. Above these comes the 

 great series of unfossiliferous slates which occupj r the whole ground 

 to the coast ; and above them the sandstones, slates, and conglo- 

 merates of Dinas Head. 



With regard to the graptolitic shales, the stratigraphical evidence 

 and the occurrence of Siphonotreta micula in beds immediately 

 below them suggest that they belong to some horizon above the 

 Llandeilo ; for elsewhere, as already mentioned, this brachiopod 

 occurs with the typical Upper Llandeilo trilobite Ogygia Buchi. 

 The identification of the graptolites, which Prof. Lapworth kindly 

 undertook, tends to confirm this view. The greatly compressed state 

 in which they occur renders them very difficult of identification, 

 but the following three forms seem to be represented : Diplograptus 

 euglyphus (Lapworth), D. folia ceus (Murch.), large form, D. trunca- 

 tus (Lapw.), or D. perexcavatns. 



According to Prof. Lapworth, these appear to be Upper Glenkiln 

 forms, and to belong to a very conspicuous zone in South Wales 

 occurring close below, or in the immediate neighbourhood of the 

 well-known Bala Limestone. At any rate, they are certainly of 

 Bala or of the very highest Llandeilo horizon. 



Thus is fixed the age of the beds immediately overlying the upper 

 volcanic series. The latter, therefore, must be at the base of the 

 Upper Llandeilo, and the Middle Llandeilo must be represented by 

 some of the underlying slates, unless it has completely thinned out. 

 That it is thin in this area is indicated by the succession in Good- 

 wick Bay. It is possible that it is wholly or partly represented by 

 the volcanic series, but this seems extremely improbable, since in 

 the adjacent area of Abereiddy Bay there was a complete cessation 



