I08 NATURAL SCIENCE. August, 1894. 



question were laid down in the long recordless period which followed 

 the close of the Eocene, when England for the last time " arose from 

 out the azure main." As no deposits of any value as a time scale 

 have been left in this district for this period, it is unfortunately only 

 too possible that we may never be able to arrive at a more exact 

 determination of the date of the Thames and its northern tributaries. 



PRINCIPAL REFERENCES. 



1. W. Whitaker. — " The Geology of London and of part of the Thames Valley." 



Mem. Geol. Siirv. 2 vols. 1889. {See especially pp. 183-194, 281-294, 299- 

 303,447-449, 496-499.) 

 "W. Whitaker. — " The Geology of Parts of Middlesex, Hertfordshire, 

 Buckinghamshire, Berkshire, and Surrey." Mem. Geol. Surv., explan. 

 sheet 7, 1S64. 



2. J. Prestwich. — " On the Relation of the Westleton Beds or Pebbly Sands of 



Suffolk to those of Norfolk and on their extension Inland ; with some 

 observations on the period of the final elevation and denudation of the 

 Weald and of the Thames Valley, etc." Quart. Journ. Geol. Soc, vol. xlvi., 

 1S90, pp. S4-181, pis. vii., viii. 



3. H. "W. Monckton and R. S. Herries. — " On some Bagshot Pebble-Beds 



and Pebble Gravel." Proc. Geol. Assoc, vol. xi., 1889, pp. 13-23. 

 4. "On some Hill Gravels north of 



the Thames." Ibid., vol. xii., 1891, pp. 108-114. 

 5. and H. B. Woodward. — 



"Excursion to Brentwood." Ibid., vol. xii., 1891, pp. Ixii.-l.wi. 



6. H. Hicks. — " On some recently exposed Sections in the Glacial Deposits at 



Hendon." Quart. Journ. Geol. Soc., vol. xlvii., 1891, pp. 575-584. 



7. " On the discovery of Mammoth and other remains in Endsleigh 



Street and on sections exposed in Endsleigh Gardens, Gordon Street, 

 Gordon Square, and Tavistock Square, London." Ibid., vol. xlviii., 1892 

 pp. 453-468. 



8. T. Y. Holmes. — " The new railway from Grays Thurrock to Romford : Sections 



between Upminster and Romford." Ihid., vol. xlviii., 1892, pp. 365-372. 

 g. T. McK. Hughes. — " On the Two Plains of Hertfordshire and their Gravels." 

 Quart. Journ. Geol. Soc, vol. xxiv., 1S68, pp. 283-287. 



J. Walter Gregory. 



