"Vol. 63.~] OKIGIN OF CERTAIN CANON-LIKE VALLEYS. 499 



up to some subsequent stream like the present Bay, would, it may- 

 be thought, have captured the high-level transverse river and have 

 diverted its flow to the north-east. No such difficulty arises if 

 we regard the plateau-gravels of Oxford and the Goring region as 

 deposited by water escaping from a lake formed by the blocking 

 of the Buckingham valley by the ice-sheet. 



Buckland attributed the Bunter Drift to currents of diluvial 

 violence. Such might conceivably have existed in the form of an 

 overflow from Glacial lakes occupying the basin of the Tame, or that 

 of the Avon. No indications exist, however, of canon-like channels 

 crossing the joint watershed of those rivers, or of that of the Stour 

 and Evenlode, and cut down to base-level, which we ought to find 

 if such had been the case. Lucy, on the contrary, invoked the aid 

 of ice-action ; there seems to me to be a considerable amount of 

 evidence in favour of that view. 



At Exhall, 4 miles north of Coventry, for example, near the 

 300-foot contour, are some large brickworks showing Glacial till, 

 containing not only Bunter pebbles and boulders of Carboniferous 

 sandstone, but also a number of blocks which Mr. B. H. Bastall 

 has recognized as Nuneaton diorite. The area from which the latter 

 could have been derived is very limited ; the occurrence of Boulder- 

 Clay with such erratic points, therefore, in my opinion to the 

 former existence of an ice-stream from the Pennines, moving 

 southwards along the Nuneaton ridge towards the basin of the 

 Avon. 



The Cretaceous Drift. 



The introduction of Cretaceous detritus into the Avon basin, 

 moreover, can only have been due, I think, to the action of 

 land-ice. 



It has been long known that a branch of the great Eastern 

 Glacier extended as far as Bugby, bringing into that region Chalky 

 Boulder-Clay, always containing hard chalk and grey flint of the 

 Lincolnshire type, with red chalk which must have come from the 

 Wolds. Last year I discovered at Stockton, about 350 feet above 

 sea-level, 8 miles south-west of Bugby, another characteristic 

 exposure of the same deposit, containing, with the usual Cretaceous 

 and Jurassic detritus, two big erratics, identified by Mr. Bastall 

 as Leicestershire granophyre 1 ; and I subsequently found in a garden 

 at Stratford-on-Avon, 15 miles farther to the west-south-west, 

 another boulder of the same rock, measuring 2-Jx 1| X 1| feet. 2 



Grey flint of the Lincolnshire type occurs also at Hatton, near 

 Warwick (about 350 feet O.D.), in the Triassic Drift of that region ; 



1 The famous Stockton erratic, 4 feet long, is said to be of Mount-Sorrel 

 granite : possibly this may be an error ; but, as it is enclosed with iron railings, 

 I could not ascertain. 



2 Mr. E. M. Bird, the owner of this boulder, informed me that he remembers 

 it being taken from a gravel-pit near his house. 



