C— GEOLOGY. 59 



In the immediate neighbourhood of the Bristol Channel the Keuper 

 division only is represented ; the Bunter and Permian rocks which occur 

 farther south in Devonshire are wanting, and it is not improbable that 

 much of the lower part of the Keuper is also missing. The erosion of the 

 uplifted Palaeozoic rocks must have commenced immediately after the 

 Armorican folding, and continued until their worn-down remnants were 

 covered by the Keuper sediments. It is interesting to speculate what 

 became of the material which was removed from the area during the earlier 

 stages of the New Red Sandstone. Although it is probable that Triassic 

 sediments extend under later Mesozoic strata for about 50 miles eastward 

 from the Channel, it is unlikely that either Permian or Bunter is present. 

 Farther north the latter formation occurs, however, in great force under 

 the Cheshire plain, but is overlapped southward under the Midland Trias 

 plain. In Devonshire also, the Bunter is believed to be represented as well 

 as certain older red rocks which are attributed to the Permian. 



We must suppose that during these earlier periods the products of 

 erosion were either swept northward towards the Cheshire plain, and 

 there deposited, or eastward towards East Anglia and the south-east of 

 England, whence they were removed by erosion during the later Mesozoic 

 period and transported to areas outside the British Isles. On the whole, 

 it appears probable that much of it found its way into the great New Red 

 Sandstone basin which lay to the north of the east-west ranges of the 

 Armorican mountains. The rocks of the Bristol Channel area may then 

 have contributed in an important degree to the deposits of the Cheshire 

 Plain, the Midlands and the north-east of England. The study of the 

 mineral constituents of the New Red Sandstone of those areas may throw 

 some light upon this question. It is on the whole improbable that there 

 was a drift of materials southward from the Channel region. Those who 

 have investigated the New Red deposits of Devon have found evidence 

 that the prevailing direction of transport was northward. This is also 

 borne out by the finding of pebbles containing marine Upper Devonian 

 fossils in the Trias of the Midlands. 



The Triassic rocks of the Vale of Glamorgan consist mainly of a 

 Dolomitic conglomerate containing for the most part pebbles of Carboni- 

 ferous Limestone and occasional pebbles of other rocks. It rests upon the 

 denuded edges of strata ranging from Old Red Sandstone to Pennant 

 Sandstone. The underlying surface is somewhat uneven, and in places 

 the Trias is banked against scarps and hills of limestone, some of which 

 were not submerged until the Lias period. Strahan remarks that ' then, 

 as now, the Carboniferous Limestone formed scarps and the Old Red 

 Sandstone stood up as rounded hills. '^ At Llanharan, on the north side 

 of the Vale, the base of the Keuper at an altitude of about 350 feet is in 

 contact with the Pennant Sandstone. Here the Keuper, which consists 

 of breccias, ' ends ofi against a steep Pennant scarp and can scarcely have • 

 extended many yards beyond.'* At this point the escarpment rises to 

 nearly 900 feet on Mynydd y Garth, and there is little doubt that the 

 angle at its base in which the Keuper rests is a feature due to Triassic 



^ Strahan. ' The Country around Bridgend,' p. 22. Mem. Geol. Survey. 

 ' Strahan, op. cit., p. 23. 



