44 MR. Gr. BARROW 0^ T THE CORRELATION OE THE [vol. lxxv, 



4. Xotes on the Correlation of the Deposits described in 

 Mr. C. J. Gilbert's paper with the Htgh-Level Gravels 

 of the South of England (or the London Basin). By 

 George Barrow, F.G.S., M.I.M.M. (Read January 22nd, 

 1919.) 



These deposits being clearly post-Eocene, the question arises, what 

 is their true age, and with what other similar deposits within or 

 near the London district can they be correlated ? Their height 

 above sea-level — 550 feet — suggests that they form part of the 

 series of High-Level Gravels, described by various authors under 

 various names, often that of the locality at or near which they 

 occur. 



Under the heading of 'Pebble Gravel,' Mr. Whitaker has given 

 a short but good description of these l deposits, followed by a list 

 and a brief account of the numerous occurrences of pebble-gravel. 

 Unfortunately, the term has been applied by many of the observers, 

 whose notes he quotes, to deposits that have no connexion with the 

 particular gravels to which he personally restricts the use of this 

 name, so that much of the account is either of no A'alue or mis- 

 leading. The late Prof. T. McK. Hughes grasped the significance 

 of their extent and mode 2 of occurrence, being especially impressed 

 b}' their uniform level in the area surveyed by himself in Hertford- 

 shire, a little over -100 feet above sea-level. He called them the 

 1 Gravels of the Upper Plain,' and considered that they must be 

 marine. 



On the north side of the Thames, the most extensive spread of 

 these gravels occurs on the Tertiary Ridge, about Stanmore 

 Common, Shenley, Barnet, Potters Bar, etc., and these are taken 

 by Mr. Whitaker as the type occurrences. Recently these occur- 

 rences have been re-examined and re-mapped by the officers of the 

 Geological Survey, mostly by Mr. R. W. Pocock, under the 

 supervision of the writer. Brief summaries of the results have 

 been published in the ' Summary of Progress of the Geological 

 Survey.' 3 



These occurrences are especially interesting, and were selected by 

 me in my Presidential Address to the Geologists' Association 

 (191 S), 4 as giving the key to the study of the High-Level Gravels 

 on the north and north-west of London, which I believe are of 

 Pliocene age. They illustrate the fact that there are present 

 in this area two distinct types of gravels, other than river-gravels, 

 that contain stones foreign to the district. The best known are 

 the fluvioglacial gravels, which contain abundant pebbles and 



1 Mem. Geol. Surv. 'Geology of London" vol. i (1889) pp. 290-96. 



2 Q.J. G. S. vol. xxiv (1868) pp. 284-85. 



3 Mem. Geol. Surv. ' Summary of Progress for 1913 ' 1914, pp. 32 et seqq. 



4 Proc. Geol. Assoc, vol. xxx (1919) pp. 1-48. 



