494 ME. E. W. HARMEK Off THE [1S~0V. I907,. 



The distribution of the Hessle Clay, according to S. Y. Wood, is 

 shown in his Drift-map in 1867. 1 Mr. Jukes-Browne's views are 

 embodied in maps which accompany the papers named below. 2 The 

 ridge of Boulder-Clay at Stickney and Sibsey, which projects across 

 what I believe to have been the south-eastward movement of the ice 

 of the intensely Chalky Drift, belongs, in Mr. Jukes-Browne's 

 opinion, together with that of the Spilsby district, to the later or 

 Hessle stage. 



VIII. A SUGGESTED LAKE OxEOED AND THE GoEING GAP. 



The pre-Glacial Course of the Thames. 



The features of that part of the Jurassic plain which lies east 

 and west of Oxford, and those of its outlet through the Chalk- 

 escarpment, the well-known Goring gap, are so nearly identical 

 with the cases before discussed as to suggest primd facie that they 

 originated in a similar way. PI. XXXIV shows another lake-like 

 area of depression, drained by a gorge of modern aspect, excavated 

 transversely across the adjacent range of hills, and cut down to 

 the level of the plains on either side of the latter, the only case of 

 the kind in the Chalk- escarpment over a distance of 150 miles. 3 

 The deepest part of the basin is near the trumpet-shaped entrance 

 to its outlet, as at Malton and elsewhere ; it appears to connect itself 

 moreover with a district, the drainage of which was obstructed by 

 the advance of the ice-sheet. 



The basin in question is bounded on the north-east, between 

 Buckingham and Leighton Buzzard, by a transverse ridge of com- 

 paratively high land, from 400 to 500 feet above sea-level — partly 

 composed, however, of Glacial Drift, the terminal moraine of the 

 Ouse branch of the great Eastern Glacier. At present, this ridge 

 marks the division between the drainage-system of the Upper Thames 

 and that of the Fenland, but (as before suggested) the watershed 

 may have lain farther to the south-west in pre-Glacial times, the 

 Oxford plain then standing at a somewhat higher level than it now 

 does. 



Some deep borings at Hitchin 4 and at Newport (Essex), 5 revealing 

 Glacial drift at a depth of 68 feet in the one case, and 140 feet in 

 the other, below Ordnance-datum, point to the existence in pre- 

 Glacial times of valleys descending obsequently from the Chalk- 

 escarpment. 



1 Published for the first time in Proc. Yorks. Geol. Soc. vol. xv, pt. ii (1904) 

 pi. xlviii. 



2 Quart. Journ. Geol. Soc. vol. xxxv (1879) fig. 1, p. 399, & vol. xli (1885) 

 fig. 1, p. 115. 



s The case of Goring Gap is absolutely unique. At no other point south of 

 the Little Ouse-Waveney depression does water flow through the Chalk-range 

 from one side to the other. 



4 From information kindly supplied by Mr. W. Hill, F.G.S. He has since 

 written to say, that evidence has been obtained which enables him to trace this 

 consequent pre-Glacial valley for a distance of 7 or 8 miles from south to north. 



5 Quart. Journ. Geol. Soc. vol. xlvi (1890) p. 334. 



