140 Reports and Proceedings. 



but their general level does not get much lowered by snbaerial denudation. There- 

 fore, in considering the western drainage area of the ancient Severn, it was important 

 to fis the age of these plains. He did not agree with Prof. Eamsay that the 2000 feet 

 plain was pre-Carboniferous, as the Carboniferous and Old Eed hills of S. 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 

 considered as the basement-bed of the Oolitic series, was evidently formed round 

 the margin of that old land, whereas had this plain existed there would not have been 

 land sufficiently high to have arrested the Oolitic sea during the period of greatest 

 submergence; and a conglomerate implies a near shore. The absence of a coarse 

 shore -deposit at the 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-feet plain was formed ; and so 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 Chalk 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 along the sam^^ lines as that of the modern easterly streams. 

 He pointed out that the great WN.W. disturbances — many, if not all, of which'were in 

 part Post-tertiary — must be taken into account in this inquiry ; e.g., the synclinal 

 of central Devon running into the English Channel near the Isle of Wight ; the 

 anticlinal of the Bristol Channel and the Weald, which we know was a barrier 

 in pre-Carboniferous times, from the different character of the Coal-measures of 

 Wales and Culm-measures of Devon ; Mr. Godwin- Austen's ridge bringing up the old 

 rocks under London ; the barriers which caused the Lower and Upper Silurian of 

 S. Wales to differ so much from^ those of N. Wales and the Lake -district, and were 

 the indirect cause of the bosses of Silurian rocks which project through the newer 

 rocks in Central England ; the barriers that divided the northern coal-fields ; the 

 Craven Faults and the great valley which runs along them,— these and many others 

 have obviously affected recent denudation. A slight tilt to the west would send the 

 drainage again to the west along some of them ; and the question involved the 

 consideration of all traces of such changes of leveL 



Prof. Duncan observed that one important point in the paper was the hypothetical 

 dip of the Chalk, on which the existence of the Severn was made to depend ; and 

 commented on the denudations which must have taken place during the Glacial and 

 Pliocene period. He differed from the author in his view of the character of the 

 Oolitic period, which he regarded as one of great oscillation. As to the amount of 

 Palaeozoic land-surface in Cretaceous times, he maintained that the purity of the 

 Chalk deposits and their freedom from any terrestrial waste bore evidence of the 

 distance of the land at that time. The depth of the sea in which they were formed 

 was immense ; and in the Upper Cretaceous period the oscillations were also great. 

 He disputed the fact of the Miocene period of Europe having been continental in 

 character, especially as regards the upper and middle parts of the deposits, in which 

 Corals abundantly occurred. The elevation of the Alps was, he maintained, of a 

 slow progressive character, which could hardly have effected so great an area as 

 supposed by Prof. Eamsay. 



Mr. Evans called attention to the relation of the present flow of many rivers to the 

 last elevation of the land at the close of the Glacial period. The deposits of the 

 Severn valley, he thought, proved its preglacial origin, and consequently supported 

 Prof. Eamsay's argument ; but the condition of the land at the close of the Glacial 

 period was also to be fully taken into consideration, as the previously existing channels 

 had in many instances been obliterated during that period. To a great extent Mr. 

 Evans agreed with Prof. Eamsay, but he would wish to see the explanation carried 

 down to a later date. 



Mr. Green remarked, in illustration of the retrogression of escarpments, that he 

 had had some opportunity of observing the process while still in progress. In the 

 Carboniferous rocks of the north of England, where the dip of some hard rock was 

 in a certain direction and it was overlain by softer strata, it was constantly the case 

 that a brook ran along the line of junction, undermining the softer beds, bringing 

 them down into the stream, and then removing them. It was thus that escarpments 

 receded. 



Prof. Morris remarked that at an early period the Alps on the south, and the 

 Cumberland mountains on the north, formed the boundaries of a sort of trough, and 

 that this to some extent must have influenced the flow of the rivers both in Britain 

 and on the Continent, He considered that the series of elevations in pre-Permian 



