Vol. 6$.~] ORIGIN OF CEKTAIX CANOX-LIKE VALLEYS. 489 



20 miles northwards from the Lincoln gap, and similar deposits, 

 often in great thickness, cover a large area to the south of Grantham, 

 the Trent basin between Lincoln and Grantham is driftless, or 

 nearly so. I suggest that Boulder-Clay may have once existed there, 

 but that it was removed during the lacustrine conditions attending 

 the retreat of the ice by the scour of the water which then swept 

 through the gorges at Ancaster or Lincoln. Later on, when the 

 erosive power of the escaping water was diminishing, the gravels 

 mentioned by Mr. Jukes-Browne might have been deposited. 



There seems to be a considerable amount of evidence tending to 

 prove the former existence of Glacial lakes farther to the south-west. 

 During a visit to Melton Mowbray in the autumn of 1906, Mr. G. W. 

 Lamplugh was kind enough to call my attention to certain stratified 

 deposits (the 'Melton Sand' of Mr. R. M. Deeley x ), which had been 

 traced at a more or less uniform level over a considerable area in 

 the valley of the "Vvreak. The idea suggested itself to me that the 

 advance of the ice upon the basin of the Soar, obstructing the 

 drainage of the former, might have caused lacustrine conditions to 

 obtain for a time in that region. Mr. C. B. Wedd has since 

 informed us that his own observations are not inconsistent with 

 such a view. 



Farther west, at Abbot's Bromley, beyond Burton-on-Trent, Mr. 

 R. M. Deeley was good enough to show me a section of laminated 

 brickearth, derived from the Keuper marls, which appears to be of 

 lacustrine origin. This again, situated at a spot out of the track of 

 the main ice-streams, may mark the site of a Glacial lake. Such 

 conditions must have existed in other parts of the glaciated areas, 

 both during the advance and during the retreat of the ice. 2 



Mr. "W. J. Harrison also points out that a Glacial lake of con- 

 siderable size existed, in North-West Leicestershire, extending from 

 Hinckley to Market Bosworth and Ashby-de-la-Zouch, indicated at 

 the first-named place by loams with which are associated boulders 

 of Leicestershire syenite brought by floating ice. 3 As before stated, 

 he believes, as I do, that the Chalky Boulder-Clay ice moved 

 down (? up) the Soar Valley past Leicester in the direction of 

 Rugby. I cannot agree with him, however, that it travelled thence 

 to Buckingham, and still less to Finchley and Romford ; it must 

 have reached those places, I think, by a more direct course from 

 the Fenland, as explained later on. 



The quartzite-gravels of the basins of the Trent and the Witham 

 are shown on the map (PI. XXXIII) by small dots. Similar 

 deposits border the valley of the former river between Newark and 

 Nottingham, 4 but I have no means of marking them. Their range 



1 Quart. Journ. Geol. Soc. vol. xlii (1886) p. 455. 



2 Similar deposits occur also in East Anglia, and (according to Mr. Deeley) 

 at other localities in the district now under discussion, loc. supra tit. 



3 Proc. Geol. Assoc, vol. xv (1898) p. 407. 



4 'The Geology of the Country around Lincoln ' Mem. Geol. Surv. 1888 

 p. 145. 



