Yol. 6S.'] GLACIAL OEIGIN OP THE CLAY-WITH-PLTNTS. 209 



the portion of the old Thames valley that is cut off betwee]i 

 Eickmans worth and the Eastern Drift near Hatfield. 



(5) The flood-waters due to the melting of the ice, aided by the 

 Thames and the Colne, produced the great flat now covered by 

 Thames gravel to the east of Maidenhead. 



(6) A new system of drainage developed on the Pluviogiacial 

 plain, shown in the lower courses of the Wye and the Misbourne. 



EXPLANATION OF PLATES XII-XIA/. 



Plate XTI. 



Sandy brick-earth, bedded. The stones are small flints. Walter's Ash, near 

 High Wj-combe, Buckinghamshire, (Geological Survey photograph.) 



Plate XIII. 



Sarsen with a vermicular surface. The stone was found broken, as shown, with 

 the fragment about 4 feet from the larger piece and separated by red 

 clay. Lee Gate, near Wendover, Buckinghamshire. (Geological 

 Survey photograph.) 



Plate XIY. 



Map of the superficial deposits of part of the Thames Basin, on the scale of 

 3-3 miles to the inch, or 1 : 209,088. 



Disctjssiojst. 



Mr. G, Baeeow remarked that some of the ideas put forward 

 by the Authors were not likely to be accepted hj everyone ; the 

 suggested change in the course of the Thames did not appeal to 

 the speaker. At the same time, it was advisable to have all the 

 Authors' views in print, so that there might be an organized 

 production of evidence for or against them. 



Mr. C. E. N. Beomehead thought that the Authors did not in- 

 tend to suggest a Glacial origin for all Clay-with-Flints, but would 

 welcome a more exact description of the distinction, between the 

 deposit described in the paper, and Clay-with-Flints in the ordinary 

 sense of the term. 



He thought that they had done valuable work in tracing the 

 distribution of Triassic pebbles, but pointed out some difficulties. 

 If these pebbles were used to trace a pre-Glacial course of the river, 

 their introduction into the Thames system could not be attributed 

 to Glacial action. Again, he considered that mention should have 

 been made of the gravel of Ashley Hill : this gravel was full of 

 Triassic pebbles ; but, on the Authors' theory, it was anomalous, both 

 in its position south of the Thames, and in its great height above 

 Ordnance datum. 



If we accept the former course of the Thames past Beaconsfield, 

 an explanation other than that adopted by the Authors is possible. 

 He drew attention to an interesting parallel in Oxfordshire, where 

 the Wilcote Valley is an old course of the Windrush, by which that 

 river formerly joined the present course of the Evenlode. In each 



