Vol. 63.~] ORIGIN OF CERTAIN" CANON-LIKE VALLEYS. 505 



laminated lake-clay, 15 feet thick, at Wolvercote, on the summit 

 of the ridge, north of Oxford, which separates the Thames and the 

 Cherwell. 1 Mr. P. Paw writes me, moreover, that he has met with 

 a bed of what he believes to be lacustrine clay, at the top of a 

 Portland-Sand quarry on Shotover Hill, overlooking Headington, at 

 an elevation of about 450 feet above sea-level. The clay was 

 unstratified, and of a light-grey or ochreous colour. 



Tracing still further the resemblance of the Oxford area to those 

 of Shrewsbury or Bristol, we find conditions of lake-cwm-gorge 

 reproduced in the former on a smaller scale near Islip, Eynsham, 

 Cuddesdon, and Iffley. 



Gravels similar to those of the high land above Goring containing 

 (together with local flint) Triassic as well as derivative flint-pebbles 

 occur also, terrace fashion, at a lower level within the gorge, as at 

 Pangbourne, and notably farther down-stream on the island-like 

 area of Tilehurst, in which Bunter pebbles are extremely common. 

 These may represent a stage in the erosion of the Oxford plain and 

 its outlet later than that of the hill-deposits before mentioned. 



The Tilehurst gravels, resembling those at Long Hanborough 

 and elsewhere, described by Mr. Pocock, as well as those along the 

 northern margin of Lake Pickering mentioned by Prof. .Kendall, 

 may possibly be like them of deltaic origin, originating at a time 

 when the great basin of the Thames formed a lake, held up by the 

 North-Sea ice. 2 The theory that such a lake may have existed at 

 some stage of the Glacial Period is not new 3 ; but it seems to me not 

 improbable, and deserves consideration in connexion with the study 

 of the suggested Lake Oxford and its outlet. 



The more important part of the evidence for the suggested Lake 

 Oxford may be summarized as follows : — 



The features of the Oxford region so closely resemble those of the 

 Yale of Pickering as to suggest that they originated in a similar way. 



In both cases the drainage seems to me to have flowed eastwards 

 in pre-Glacial times — that of the Pickering valley into the North 

 Sea, and that of the Oxford plain into the basin of the Ouse through 

 the Buckingham valley, now partly filled with Glacial Drift, but 

 then considerably wider and deeper than it is at present. 



That the Goring gorge was not in existence in pre-Glacial times 

 is shown by the occurrence in its immediate vicinity of high-level 

 gravels regarded by Prestwich, and later by Messrs. Monckton, 

 Herries, Gregory, Osborne White, and others, as well as by myself, 

 as of Glacial age. On the contrary, the escarpments and the 

 Jurassic plain separating them seem to have originated at an 

 earlier period. 



1 Quart Journ. Geol. Soc. vol. lx (1904) p. 120. 



2 It seems to me worthy of notice that no Triassic Drift occurs in the 

 southern part of the Thames basin, or south of a line drawn from Tilehurst to 

 Maidenhead ; see H. W. Monckton, Quart. Journ. Geol. Soc. vol. xlix (1893) 

 p. 308. 



3 See H. Hicks, Quart, Journ. Geol. Soc. vol. xlviii (1892) p. 46. 



