THE 



GI*:o LOGICAL MAGAZINE 



NEW SERIES. DECADE VI. VOL. L 



No. IV.— APRIL, 1914. 



CD:ElXG-XT<r J^JL. .A.I?,TIOI-.ElS. 



I. — The Chiltern Wind Gaps. 



By J. W. Gregory, D.Sc, F.E.S. 



rpHE Geological History of the Thames is still the subject of 

 X conflicting hypotheses. Mr. F. W. Harraer (1907)' has drawn 

 a very interesting parallel between the basin of the Middle Thames 

 around Oxford and the Vale of Pickering in Yorkshire. The latter, 

 as is well known, from Professor Kendall's paper (1902),^ was 

 occupied by a glacial lake which was due to the Derwent River 

 having had its outlet to the sea south of Scarborough closed by a dam 

 of ice ; the water rose in this lake until it overflowed at a gap near 

 Malton ; the river thus formed cut a gorge through which the drainage 

 from the Vale of Pickering flows south-westward into the Yorkshire 

 Ouse, and reaches the sea through the Humber. According to 

 Mr. Harraer the Upper Thames originally discharged north-eastward 

 through the Fens into the Wash ; this outlet was blocked by the ice ; 

 the waters of the Upper Thames collected as a lake, which was 

 discharged by overflow channels cut through the Chiltern Hills, and 

 as the lake-level fell the discliarge was maintained only through the 

 Goring Gap at the south-western end of the Chiltern Hills. This view 

 advances a different explanation of the Chiltern wind gaps than that 

 advocated in a paper in 1894,^ and is opposed to the theory of the 

 evolution of English rivers adopted by Professor W. M. Davis 

 in 1895.* 



The analogy drawn by Mr. Harraer between the basins of the 

 Upper Tharaes and the Vale of Pickering is very attractive ; but the 

 striking difference between the arguments for Lake Pickering and for 

 Lake Oxford is, that for the former there is abundant positive 

 evidence, while for Lake Oxford there is no such direct evidence. 

 Professor Kendall has demonstrated the changes in the course of the 

 Derwent and the former existence of Lake Pickering by convincing 

 evidence. That the Derwent formerly reached the sea through the 

 great valley south of Scarborough appears so obvious as to be almost 

 indisputable. The former existence of Lake Pickering is shown 

 by the form of the basin and the abundant deposits on its floor; and 

 the margins of the old lake are indicated by well-developed lake 

 beaches and deltas. If Mr. Harmer's Lake Oxford had been in 

 existence at about the same period as Lake Pickering — and they are 

 both assigned to the period at the close of the Uoulder-clay — we 



DECADE VI. — VOL. I. — NO. IV. ^^ ; ; IP 



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