ETC. 123 



" Doubtful Deposits," in greater detail and with some slight changes, 

 and retains the open term of " Pebbly Gravel." 



In 1867 * Mr. Searles V. Wood, Junr., called attention to the 

 relations between the Post-Glacial, Middle, and Upper Glacial 

 deposits of the Valley of the Thames, in connexion with the 

 position of the latter two on the hills and in the valleys of this 

 area. Prof. Boyd Dawkins showed, however, that his contention — 

 based on theoretical grounds, that certain valleys " could have had 

 no existence at the period of the Glacial Clay " — was not in accor- 

 dance with the Survey observations. 



In 1868 t Prof. T. M''K. Hughes described an outlier of peculiar 

 gravel he had noticed near Hertford, under the term of " Gravel 

 of the Upper Plain " in contradistinction to the " Gravel of the 

 Lower Plain." The latter he referred to the Glacial Series. Of 

 the other ho says, " From their great extent, persistent character, 

 and uniform level, I think these gravels of the Higher Plain must 

 be a marine deposit ; but without a careful examination of the old 

 coast-line, and of their behaviour as they approach the Crag country, 

 I should not like to give any opinion as to their age." He further 

 states that they were of great antiquity and older than the Boulder- 

 clay. 



Mr. Wood, commenting on this communication, contended that 

 this Gravel of the Upper Plain was of an age intermediate between 

 his " Middle Glacial" and the Boulder-clay; while the outliers of 

 other pebbly gravels at Brentwood, Highbeech, South Weald,^ 

 Langdon Hill, and others +, were " not im[)robably of Eocene age." 



Another paper of Mr. Wood's on the Wealden Denudation §, only 

 bears incidentally on this question, as showing the existence and 

 extent of Drift Beds in the Thames Valley older than the lower- 

 level Valley-gravels. 



The most important contributions to this subject by Mr. Wood 

 are, however, those in which he sums up his numerous and exten- 

 sive observations, and gives his final views on this and collateral 

 questions ||, accompanied by a map of the area occupied by the 

 Chalky Boulder-clay, and a Plate of Sections showing the ratige 

 and distribution of the Pre-Glacial, Glacial, and Post-Glacial Beds, 

 with the position and probable relation of the hill-gravels throughout 

 the south of England. The second part is devoted more especially 

 to the consideration of the Post-Glacial Beds, particularly of those 

 in the Thames and Hampshire Basins, and to the elaboration of his 

 views respecting his Periods of Depression, liise, and Glaciatiou. 

 These papers, however, are not easy to summarize, but can be con- 

 sulted with advantage. 



The reader will also find in a paper by Mr. F. C. J. Spurrell, 



^ Quart. Journ. Geol. Soc. vol. xxiii. p. 394 (1807). 



t Ibid. vol. xxiv. p. 283 (18(i8). 



+ Ibid. Tol. xxiv. p. 40)4 (ISCS). 



I Ibid. vol. xxvii. p. 3 (1871). 



jl " On the Newer Pliocene Period in England, Part I.," Quart. Journ. 

 Geol. Soc. vol. xxxvi. pp. 4o7-r)28 (18:i0) ; Part II., ibid. vol. xxxviii. 

 PP.G67-745 1882). 



