Vol. 6S.] GLACIAL OEIGIIf OE THE CLAT-WITH-FLINTS. 211 



Mr. G. W. Lamplfgh asked whither the Authors proposed to send 

 their Thames after it reached Watford. If again north-eastwards, 

 it would cross country with which he had some acquaintance. 

 But his impression had been that the quartzite-gravels of this part 

 probably belonged to a Glacial outwash-plain formed by waters 

 which flowed south-westwards from Hatfield to Watford — a direction 

 diametrically opposite to that of the supposititious Thames. He 

 considered that the Authors were hardly justified in abandoning 

 their river, without indicating whither it was to go. 



Mr. G. W. YoTJNG agreed that when one attempted to apply the 

 theory of the Glacial origin of the Clay-with-Flints to other areas, 

 one was confronted with very grave difficulties. Eor instance, in 

 Surrey the Clay-wifch-Plints occupied a large part of the high 

 ground close up to the Chalk escarpment, and it was difficult to 

 imagine whence the ice-sheet that formed it in such a position 

 could have come. If, as the Authors asserted, the northern sheet 

 was arrested by the Tertiary escarpment at Eickmans worth, one 

 was driven to suppose that the Weald must have had a separate 

 ice-sheet, which was difficult to believe. The great variability in 

 thickness and ' pocketty ' nature of the Clay-with-Flints led the 

 speaker to think that solution in situ and the letting-down and 

 commingling of Eocene material was a more satisfactory expla- 

 nation of its origin in Surrey. 



Mr. H. W. MoNCKTON said that the course of the discussion had 

 made him suspect that the Authors had included under the name 

 ' Clay-with-Elints ' some deposits which differed from those usually 

 included under the term. 



With reference to the suggested blocking of valleys by ice, he 

 wished to repeat the remark which he had often made, that with 

 regard to the stratified gravels of the district he felt convinced that 

 they were in all cases older than the valleys which adjoined them 

 and were at a lower level. He did not believe that these stratified 

 gravels had been deposited on the tops of hills. 



Dr. R. L. Sheeloce, in reply, thought that much of the criticism 

 was due to a misunderstanding. The Glacial origin was claimed 

 for the Clay-with-Flints over a limited area only, and it might be 

 that the Clay-with-Flints of other districts was a different deposit 

 formed in a different way. Mr. Whitaker's objection, that the 

 Chiltern Hills were too low to stop a great ice-sheet, loses its force 

 when we remember that the ice was not far from its southern limit. 

 The amount of Upper Chalk denuded can be estimated from the 

 known thickness of the zones, and the horizon on which the Eocene 

 rests. The boundary between the Gravelly Drift and the Fluvio- 

 glacial Gravel is fairly well marked, and only occasionally offers 

 difficulties. The Authors had not thought it desirable to make 

 any statement about the country, which they had not mapped, east 

 of Watford, and so the delineation of the course of the Thames 

 beyond that place was left for future workers. The gravel on 

 Ashley Hill, which contains Bunter pebbles, is anomalous, and has 

 not been coloured on the map. It is at a much higher level than 



