Yol. 63^ OKIGIN OF CEETAItf CANON-LIKE VALLEYS. 501 



in the Oxford gravels would have travelled together from the same 

 direction. 



When we reach the neighbourhood of Goring and the Chalk- 

 escarpment, the case is different. There the gravels contain much 

 flint, subangular or little worn, and having a recent appearance 

 when broken, which is clearly of local origin. With it, however, 

 and the abundant Bunter Drift, are found, as at Oxford, worn and 

 travelled flint-pebbles, sometimes partly decomposed, derived from 

 an older deposit. 1 They are generally stained, inside and out, 

 brown or greyish, having been worn and discoloured previously to 

 their introduction into the gravels, often whitish in colour, in 

 which they occur ; most of these, I believe, may have come from 

 the Glacial Drift. 



The Origin of the suggested Lake Oxford. 



Prestwich considered the occurrence of Triassic pebbles the 

 special feature by which Glacial gravels were to be distinguished, 

 and he consequently held that those capping the hills west of 

 Oxford, and above the Goring gorge, were of Pleistocene age. 2 



1 have stated the evidence in favour of this view at some length, 

 because it is really the crucial point of the enquiry, our opinion as 

 to the date at which the gorge was excavated depending on it. 



There seems to be little doubt that the gravels occurring above 

 and on either side of the gorge are of similar age to those of the 

 hills near Oxford which, as already shown, can be traced to the 

 Evenlode, and thence to the Glacial deposits of Warwickshire. 



Mr. H. J. Osborne White says, for example, that the Tertiary 

 outlier at Upper Basildon, west of the gorge, 466 feet O.D., is capped 

 by Glacial gravels of an unequivocal kind, 3 such deposits being also 

 found to the east of it over an area the northern boundary of which 

 more or less closely corresponds with the 500-foot contour, and the 

 southern with the Thames. 4 I have marked the distribution of 

 these higher-level gravels on the map (PL XXXIV) from particulars 

 given in his paper. Gravels of a more or less similar character 

 occur also at various levels, as well-marked plateaux or terraces 

 which, as before stated, connect themselves with the valley-deposits 

 of the present river. 5 



It may be noticed that plateau-gravels do not always occur on 

 the highest slopes of the great breach in the Chalk-escarpment of 

 which the Goring gorge forms the lower part ; an overflow 

 unattended by the deposition of gravel might have taken place 

 in the first instance, however, at the higher elevation — such 



i See also A. M. Bell, Quart. Journ. Geol. Soc. vol. k (1904) p. 129. 



2 Quart. Journ. Geol. Soc. vol. xlvi (1890) p. 150. 



3 Proc. Geol. Assoc, vol. xiv (1895-96) p. 22. 



4 Ibid. p. 16. 



5 Bunter pebbles occur also in places farther to the eastward. I have not 

 attempted to show these on the map, as they seem to have no immediate 

 bearing on the question now discussed, namely, the age of Goring Gap. 



