Corres2)ondence — Mr. S. V. Wood. 285 



Geological Magazine for February, 1870; and that the range of 

 that formation on the south side of the Cambridgeshire escarpment, 

 its overlap by the Boulder-clay resting direct on the older rocks and 

 spreading up to the top of the escarpment, and the recurrence of 

 the Boulder-clay without any Middle Glacial beneath it on the 

 opposite side of the escarpment, are most clearly shown by me in 

 section 7 of my paper in the Quart. Journ. Geol. Soc, read June 

 19th, 1867 (p. 402), which crosses the Cambridgeshire valley {i.e. 

 the great valley which, beginning about Hitchin, and stretching east- 

 wards past Eoyston to Cambridge, has its south side formed by the 

 Chalk escarpment) at about its central part, at Royston. 



^' The section just referred to is one of several sections illustrating 

 the position of the Glacial beds relatively to a series of curvilinear 

 escarpments (forming concentric arcs), of which that of the Cam- 

 bridge Chalk is one. In your paper you also point out prominently 

 that the great valley whose south side is formed by this escarpment 

 is of Pre-Glacial origin ; and, from the report of the discussion, it 

 appears that Mr. Jukes-Browne was induced by it to remark that 

 your views were in opj)Osition to those of Mr. Harmer and myself, 

 who would place the excavation of all the valleys in the Glacial 

 period ; while you considered them pre-glacial. Now in the long 

 foot-note at page 14 of my paper in the Quarterly Journal, read 

 November 9th, 1870, you will find, in reference to this and other 

 similar curvilinear escarpments, the following observation, viz. : — 

 ' I formerly supposed that these curved groups were equally with 

 the rectilinear ones of post-glacial origin; but an examination of 

 the glacial beds of Bedfordshire and Northamptonshire showed 

 these beds in such a position relatively to the Chalk and Oolitic 

 escarpments (which form concentric curves of the Canterbury group) 

 as necessitated the inference that these curves were of pre-glacial 

 origin.' 



"You will thus see that for several years I have regarded these 

 curvilinear escarpments, and (ex necessitate) the valleys in any way 

 formed by them, as of pre-glacial origin. I am not aware that Mr. 

 Harmer has ever expressed any opinion at all as to such valleys ; 

 but both he and I did, and still do, regard the general valley system 

 of East Anglia as of combined inter-glacial and post-glacial origin ; 

 but even to this there are some exceptions ; as, for instance, the upper 

 valley of the Little Ouse in Norfolk, and the valley of the Black- 

 water in Essex, which are of pre-glacial origin. 



"One important error which I made (but which does not appear to 

 have been detected) was in stating (page 417 of my paper in the 

 Quarterly Journal read June 19th, 1867), that 'every valley in the 

 south-east of England in which the Upper and Middle Glacial 

 deposits occur sufficiently near to afford evidence on the question, 

 has been formed subsequently to the Upper Glacial Clay.' My 

 subsequent working out of East Suffolk and Norfolk in conjunction 

 with Mr. Harmer showed that this was not the case, but that tlie 

 East Anglian valley system, so far as the position of the Glacial 

 series afforded evidence, originated after the Lower Glacial dej)osits, 



