Vol. 6$.] ORIGIN OF CERTAIN CANON-LIKE VALLEYS. 491 



and close to the western slopes of the Wolds, that the intensely- 

 chalky Bonlder-Clay of Lincolnshire occurs, that of the lower 

 ground a short distance only to the west being darker in colour, 

 having a Jurassic matrix, and containing much Jurassic detritus ; 

 the latter deposit was well shown in 1904 at a disused brickyard 

 near Langton. The distinction between the two kinds of Drift is 

 well marked, and has long been known. One passes abruptly, 

 moreover, from one kind to the other. 1 



Descending from the Wolds towards the plain of the River 

 Witham, the intensely-chalky Drift abruptly trends south-eastward 

 to the south of Benniworth, piling itself up in long ridges, parallel 

 to the Wold scarp, which attain in places a height exceeding 

 450 feet above sea-level ; viewed on the spot these ridges suggest 

 to me the idea of a lateral, or perhaps a medial moraine. 



Similar Boulder-Clay, whitish in colour with a chalky matrix, 

 and containing but little Jurassic detritus, apparently a continuation 

 of the intensely-chalky Drift of the Wolds, is met with in Central 

 Norfolk to the south-east of the district in question. The Chalky 

 Boulder-Clay of a great part of Suffolk, on the other hand, is blue, 

 and contains a vast amount of Kimeridgian debris, corresponding 

 with the Jurassic Drift of the Witham basin. In East Anglia, as 

 in Lincolnshire, one passes suddenly from one kind of Drift to the 

 other. Conterminous along a line running roughly from west to 

 east in the former region, these Drifts are equally dissimilar in 

 appearance and composition. Taken as a whole, they seem to me 

 to represent the morainic accumulations of distinct but contiguous 

 ice-streams travelling side by side in a south-easterly direction 

 from Lincolnshire, across the mouth of the Wash, into East 

 Anglia. 2 The only explanation that I can suggest, of the sudden 

 diversion of the Chalky Drift towards the south-east, is that the 

 basin of the Witham was then occupied by a more important ice- 

 stream, sufficiently thick to prevent the Wold ice from over- 

 spreading the lower ground. 



As the intensely-chalky Drift reaches a height of 450 feet O.D. 

 above Benniworth, and the ice which impinged against the eastern 

 side of the Cleveland Hills attained in the latter region, according 

 to Prof. P. E. Kendall, a still greater elevation, 3 an overflow from 

 the North Sea must also have taken place, I believe, through 

 the depression, 20 miles wide, separating the highest part of the 

 Lincolnshire Wolds from those of Yorkshire, where the Chalk ridge 

 is much broken up and rarely exceeds 300 feet in height. It was 



1 In places, however, the ice of the intensely-chalky Boulder-Clay seems 

 to have encroached on that of the Chalky-Jurassic Drift, the former deposit 

 being sometimes found in well-borings to be underlain by Boulder-Clay of a 

 dark-blue colour. 



2 I hope to give further evidence in favour of this view, in a future paper. 



3 See his map of the glaciers and glacier-lakes of the Cleveland area, Quart. 

 Journ. Greol. Soc. vol. lviii (1902) pi. xxviii. 



