1872.] EAMSAT EIVEE-COTJBSES OF ENGLAND AlTD WALES. 157 



Cardiganshire, Caermarthenshire, part of Pembrokeshire, and in 

 parts of other adjacent counties is, I consider, of older date than the 

 Carboniferous strata ; and I also consider that great part of that 

 ancient Silurian tableland was overspread by these strata. On 

 their removal by denudation, that tableland was attacked by all 

 the ordinary powers of waste ; and now, a modified descendant of a 

 pre-Carboniferous plateau, it is traversed by unnumbered valleys 

 and streams that run towards every point of the compass, mostly 

 across the strike of the strata, but some, like the Towey of Caer- 

 marthenshire, and the Teivi of Cardiganshire, along the lines of 

 strike for long parts of their courses, where comparatively soft slates 

 and Llandeilo flags form the surface, bordered by hills formed of harder 

 rocks. Some of the rivers, like the Wye and the Usk of South 

 Wales, run right through bold escarpments, in the manner of the 

 Thames ; and similar cases in North Wales are not wanting. But 

 this part of a very large subject I hope to return to in a future 

 paper, should I find time to prepare it. 



Discussion. 



Mr. Hughes pointed out that in Wales and the Lake-district, which 

 in this question might be considered as one, there were two plains of 

 marine denudation — the one referred to by Prof. Ramsay averaging a 

 little over 2000 ft., and the other about 3000 ft. above the sea. Such 

 plains get eaten back and cut up into valleys; but their general level 

 does not get much lowered by subaerial denudation. Therefore, in 

 considering the western drainage-area of the ancient Severn, it was 

 important to fix the age of these plains. He did not agree with 

 Prof. Ramsay that the 2000-ft. plain was pre-Carboniferous, as the 

 Carboniferous and Old Red hills of South Wales and, in a more marked 

 way, those of West Yorkshire and the Lake-district were evidently 

 cut down by the same denudation that planed off the top of the 

 Silurian area, and their tops formed part of the same plain. He 

 did not think that this plain could be even pre-Oolitic ; for the 

 shingle-beach of the Trias, which might be regarded as the base- 

 ment-bed of the Jurassic series, was evidently formed round the 

 margia of that old land, whereas had this plain existed there would 

 not have been land sufficiently high to arrest the Jurassic sea 

 during the period of greatest submergence; and a conglomerate 

 implies a shore near. The absence of a coarse shore-deposit at their 

 base, and the character of the Cretaceous deposits, also would lead 

 him to infer that the Chalk-sea probably washed no land so near as 

 Wales ; but it was quite possible that the chalk was removed from 

 the Welsh area when the 2000-ft. plain was formed ; and in that 

 case we should refer the initial Severn to the time when the deposits 

 of the sea that formed that plain were being eaten back, and not to 

 the time when the Chalk was being removed. He asked where 

 were the valleys when the drainage of the eastern area ran west 

 into the Severn, as there was considerable difficulty in supposing 

 that the main westerly drainage was in reverse direction along the 



