I.—The Chiltern Wind Gaps

Abstract

The Geological History of the Thames is still the subject of conflicting hypotheses. Mr. F. W. Harmer (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. Harmer 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 discharge 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.