508 MR. F. W. HARMER OK THE [Nov. I907, 



c Westleton Beds ') with those grouped as Glacial and coloured 

 pink on the Geological-Survey maps of the East of England. The 

 breaching of the Chalk-escarpment, with the erosion of the series 

 of north-west to south-east valleys trenching it, including the 

 Goring canon, took place, he thinks, between the formation of 

 these gravels and the advance of the ice-sheet — the face of the 

 escarpment then extending farther to the north-west. 



As I do not wholly agree with Prof. Gregory's premises, and 

 as my general explanation of the facts differs from his, it may be 

 desirable to state shortly my own views on the giaciation of the 

 district in question. 



Dealing with the subject as a whole, I do not think it possible 

 to separate the Glacial gravels from the Boulder-Clay ; I believe 

 that they originated more or less contemporaneously. 



During the advance of the ice-sheet, streams of water issued 

 from its front, causing local deposition of fluvio-glacial sand or 

 gravel, much of it being destroyed by the advancing ice ; but, as the 

 thickness and erosive power of the latter decreased, it moved over 

 a cushion of Boulder-Clay, part of a mudbank which it was pushing 

 before it, the underlying gravels being thus protected from dis- 

 turbance. l Near the farthest extension of the ice-sheet and beyond 

 the point to which Boulder-Clay was carried, masses of coarse 

 morainic or fluvio-glacial gravel accumulated, as in the neighbour- 

 hood of Buckingham. 2 Similar gravels, the ' Cannon-shot' deposits 

 of East Anglia, were deposited sporadically during its retreat. 



Generally, such gravels are found overlying the Chalky Boulder- 

 Clay, but they sometimes occur beneath it, always containing 

 detritus similar to that of the Boulder-Clay associated with them. 

 The gravel of one place may be, therefore, of the same age as the 

 Boulder-Clay of another. Although doubtless representing a period 

 of many thousand years, these deposits belong, I consider, to one 

 series of events, that intervening between the advance and the 

 retreat of the ice. The material of both gravel and Boulder-Clay 

 came from the same sources, and presumably during the same 

 period. 



The distribution of the Chalky Boulder-Clay and the fluvio- 

 glacial gravels is shown on the map (PI. XXXIV). 



It appears that a branch of the great Eastern Glacier, that 

 to which the Chalky Boulder-Clay was due, moved up from the 

 Eenland in a mighty stream, 40 miles in width, which not only 

 filled the basins of the Welland, the Nene, and the Ouse to the 

 brim and overflowed the higher ground separating them, but heaped 

 up its terminal moraine on the amphitheatre of low hills forming 

 the south-western boundary of the region. 



1 Prof. Chamberlin says that this is what is taki mg place in Greenland, Bull. 

 Geol. Soc. Am. vol. vi (1895) p. 214. See also S. V. Wood, Jun., Quart. Journ. 

 Geol. Soc. vol. xxxvi (1888) p. 487. 



2 See the illustrations in A. H. Green's ' Geology of the Country around 

 Banbury, &c.' 1864, Mem. Geol. Surv. Sheet 45, figs. 12-15. 



