1866.] WHITAKER LOWER LONDON TERTIA.RIES. 407 



Thanet Beds and the Chalk in East Kent*. Is it not possible that 

 this also may be owing, to some extent, to the infiltration of waiter 

 along the line of jnnction, and that the dissolving away of the chalk 

 by the water may have been stopped, or regulated, by the continuous 

 bed of flint which there occurs directly below the base-bed ? I do 

 not mean to say that this can have taken place since the elevation 

 of the country to its present position, but would suggest that such 

 an action would not be impossible when the beds in question were 

 many hundreds of feet lower, and therefore saturated with water 

 throughout, and subjected to great pressure from overlying materials. 

 Should this be true, it will be a case of the same action causing 

 exactly opposite results under different conditions ; the infiltration 

 of water through the Tertiary beds to the Chalk now (when com- 

 paratively small) causes unevenness (pipes) at the junction, at least 

 where that junction is near the surface, whilst it may have caused 

 evenness when of far greater extent and when the junction was at 

 a great depth. 



Since the above was written, I have found that my coUeague Mr. 

 Hughes has come to a more decided opinion as to the formation of 

 the bed of green-coated flints after the deposition of the Thanet Beds, 

 and that he has gone into the question in greater detail than I have, 

 as may be seen from his paper (p. 402). 



Mr. Codrington, in the essay before noticed, has come to the con- 

 clusion " that the origin of the clay-with-flints is to be ascribed to 

 the gradual dissolving away of the chalk-with-flints under a capping 

 of drift hricIc-eartJi" " 



Just after this paper was read, Mr. Dowker published a note on 

 the junction of the Thanet Beds and the Chalk f, in which he sug- 

 gests that the bed of green-coated flints may be the result of the 

 subaerial dissolution of the Chalk before the deposition of the Thanet 

 Beds. I can hardly agree with this view, but look with more 

 favour on my friend's idea, that the tabular layer of flint at the top 

 of the Chalk may have been formed after *the deposition of the over- 

 lying beds, and the more so as he has in his collection a specimen of 

 a green-coated flint partly enveloped in a piece of the whitey-brown 

 tabular bed. The same idea occurred also to Mr. J. Evans, E.R.S., 

 who spoke to me (before the publication of Mr. Dowker's note) of 

 the possibility of the layer in question having been thus formed. 

 This flint-layer occurs further west than is stated in my former 

 paper, and may be seen at Grays and Purfleet. 



Mr. Prestwich has inferred that the layer of unworn green-coated 

 flints, which nearly everywhere rests on t' e top of the Chalk where 

 it is covered by Tertiary formations, is e\ ..jLywhere of the same ^get. 

 This may be the case ; but it is remarkable that where the Thanet 

 Beds are present, the Chalk never (as far as I know) shows those 

 holes of boring mollusks so common where the Beading Beds he 

 directly on it, and the occurrence of which at Kembridge, jS"ewbury, 



* Quart. Journ, Geol. Soc. vol. xxi. p. 397. 

 t G-eol. Mag. for May 1866, vol. iii. pp. 210, 239. 

 X Quart. Journ. Geol. Soc. vol. viii. pp. 241, 252, 253, 

 VOL. XXII. — PART I. 2 P 



