io8 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. Surv. 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, 1864. 



2. J. Prestiflfich. — " 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., 

 1890, pp. 84-181, 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." J6/^., vol. xii., 1891, pp. 108-114. 

 5. and H. B. Woodward. — 



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

 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." Ibid., vol. xlviii., 1892, pp. 365-372. 



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



Quart. Journ. Geol. Soc, vol. xxiv., 1868, pp. 283-287. 



J. Walter Gregory. 



