22 PROCEEDINGS COTTESWOLD CLUB 19 lo 



Concerning the Wenlock, it may be as well to state that in this part of 

 Wales it is almost wholly shale, and therefore imlike its equivalent in many 

 other parts, where its upper and lower portions are limestone — the Wenlock and 

 Woolhope Limestones respectively. This absence of limestone from the Wen- 

 lock and succeeding Ludlow Stages presented a difficulty to the earlier geological 

 cartographers, who, in the lack of more definite pala^ontological knowledge, 

 were wont to rely frequently upon lithological characters when mapping the 

 distribution of the rocks. Errors were made ; and frequently — owing to no 

 parting mass of limestone — Wenlock and Lower Ludlow beds were mapped 

 as one formation, and correlated with the Wenlock Stage of certain other 

 parts, the so-called "Ludlow" of the geographical maps of the Welsh 

 Borderland being in consequence paralleled with the Upper Ludlow of such 

 typical areas as that of Shropshire. But now, as was anticipated by Prof. 

 Charles Lapworth, by the aid of the lowly graptolite, the geologist is able to 

 read off with ease and certainty the true succession in the monotonous 

 Silurian mudstone of Great Britain, and to effect correlations that were 

 denied to the earlier workers in this particular branch. 



The Carneddau formed a land-mass while the Gwastadcn and Caban 

 Groups and Upper Llandovery Beds were being deposited, but disappeared 

 beneath the Ludlowian sea. The Carneddau and Gilwern Hills obviously 

 mark an area of crust-weakness, the presence of which is clearly indicated in 

 the present-day geographical distribution of the Wenlock and Ludlow rocks. 



South and south-west of Builth-Wells is the furrowed upland called the 

 Mynydd Eppynt, which is capped with the lower beds of the Old Red 

 System, whose higher strata form the jagged Brecon Beacons and the no less 

 awe-inspiring Carmarthen Fan. 



It cannot be determined for certain whether or not any post- Devonian 

 rocks were laid down over the Builth district. Certain it is that for untold 

 ages these Palaeozoic rocks have been undergoing subaerial denudation. 



After tea, the weather improved, and under the guidance of the Rev 

 Edmondes Owen, of Llanelwedd, the Members made the ascent of the 

 Carneddau. 



Mr Owen first pointed out a well-preserved cock-pit, and then, higher up 

 the hill-side, the foundations of a Celtic hut and a kist. Mr Owen indicated 

 a small excavation in front of the entrance to the hut, which had juovcd the 

 presence of charred wood that had been burnt, and a short distance beyond a 

 well-preserved kist, whose opening he had himself superintended. Mr Owen 

 remarked that the tumulus had been constructed on a roughly-pavcdjarea, 

 and was surrounded by a circle of large stones. After Mr Owen had finished 

 speaking, the Hon. Secretary pointed out the geography of the country within 

 view, and made some remarks upon the phases of development at which the 

 river-systems of Central Wales had arrived. Upon this subject he gave 

 a lecture later on in the evening at the hotel. ' Some of the Members 

 climbed up to the Caer Fawr, from which they saw also another hill-fort, 

 Caer Einon. Caer Fawr and Caer Einon are large bosses of igneous rock that 

 have had their more readily accessible sides protected with works of earth and 

 stones. Caer Einon is the more instructive, the ramparts of stones being 

 very conspicuous, as well as the entrance and the old road leading up to it. To 

 the north of Caer Fawr is a basin-like depression, which is occupied by 

 a small tarn that is fast becoming filled up with vegetation — cotton-grass 

 being very conspicuous. The linguiform depression that runs southwards 

 from this tarn has been caused by the Llandeilo Shales between the igneous 

 masses weathering much more rapidly than their flanking harder rocks. 



I The subject is fully dealt with in a paper in the Geological Magazine for November, 1909. 



