502 ME. F. W. HAEMEE ON THE [Nov. I907, 



deposits accumulating near the margin of the stream when it began 

 to cut itself down to a lower level. 



Applying Prof. P. F. Kendall's hypothesis to the Oxford region, 

 we shall find that it offers a possible explanation of the facts. 



It does not appear that the Cretaceous and Jurassic escarpments 

 differed materially, either in form or in position, in Pleistocene 

 times. The general features of the Triassic and Jurassic plains 

 had been then sketched out, initiating and directing the move- 

 ments of the ice, although erosion must have taken place locally 

 during the advance of the latter, and subsequently, when it melted. 

 Glacial deposits are constantly found within the valleys, extending 

 to the level of the alluvium, or below it, as well as mantling 

 the slopes of the hills, and bedded up to and against the face of the 

 escarpments. 



The distribution of the Chalky Boulder-Clay, to be discussed 

 more fully later on, shows that the advance of the great Eastern 

 Glacier from the north-east, extending from the Northampton 

 Uplands to the East Anglian ridge (see map), must have arrested 

 any drainage then flowing towards the "Wash, the ice having been too 

 thick, I consider, to have permitted an outfall in that direction. 

 On the view here taken, a lake would have come into existence, 

 its overflow possibly taking place at first through the Newport 

 valley into that of the Stort, or by the Hitchin valley into the 

 Lea. 1 The forward movement of the ice may have been too 

 rapid at that time to allow of the excavation of gorges in this 

 area like that of Goring. 



"When eventually the ice reached Buckingham, such channels 

 would have been closed, the suggested overflow taking place farther 

 to the south-west. 



The valley of the primeval Thames (or Isis), then, I submit, 

 leading to the Wash, would have been the first part of the Oxford 

 plain to assume lacustrine conditions ; but, unless the Corallian 

 escarpment, before mentioned, had been already broken up into 

 isolated hills as it now is, gaps would have been formed in it 

 by the diversion of the drainage towards the south, one of 

 them coinciding with the north-and-south valley in which Oxford 

 stands. Either the Triassic gravels capping the hills west of that 

 city mark the approximate level of the Oxford plain during the 

 Glacial Period, which seems to me improbable, or they indicate 

 the height at which water first crossed the Corallian escarp- 

 ment, just as the plateau-gravels near Goring may represent an 

 early overflow of the Chilterns. 2 Sooner or later an escape from 



1 Some of the brickearths of the Hitchin Valley may possibly be of lacustrine 

 origin. 



2 Assuming that lacustrine conditions obtained in this region in Glacia 

 times, the lake would have been frozen over in winter, possibly to a consider- 

 able depth. Gravel might therefore have been carried over the ice across the 

 Oxford plain to the Corallian escarpment, or the Goring gap, and deposited at 

 a high level by floods descending from the Cotteswolds in spring before the 

 lake-ice had disappeared. 



