76 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Woolwich, and Bromley. Some of the principal sections in these 

 localities have been described by Parkinson*, Webster f, Dr. Buck- 

 land J, Phillips and Conybeare§, Morris ||, Mitchell**, Richardsonft, 

 Warburton JJ, and more recently bythe Rev. Mr. De la Condamine§§ ; 

 whilst outlines of some underground sections have been planned by 

 Mr. R. W. Mylnellll, and a short notice relating to the superposition 

 of these and the other Tertiary strata has lately been given by M, 

 Hebert***. But nevertheless the correlation of the beds at the 

 different sections has not, I conceive, been correctly shown, and the 

 position which the strata of the Reculvers and Heme Bay hold with 

 respect to those of Woolwich and Reading yet remains luisettled. At 

 the same time, the lists of fossils even at the several best-knowTi and 

 often-explored localities admit of many additions and corrections. 

 From the very circumstance of the band of green sand with the Os- 

 trea BeUoimcinajVfhich underlies the mottled clays at Reading, having 

 been referred to the band of green sand at the base of the Thanet 

 Sands at Woolwich, and which likewise reposes upon the Chalk, it 

 has had a tendency to place the Mottled Clays too low with respect 

 to the fluviatile beds of Woolwich, and rather to correlate these latter 

 with the Basement Bed of the London Clay at Reading. There was 

 however another reason for this arrangement, inasmuch as in the 

 sections at Blackheath, and elsewhere near London where the mot- 

 tled clays show themselves, these latter underlie the Woolwich shelly 

 clays ; but, as will be shown further on, this relative position is not 

 permanent, for another and larger portion of the " mottled clays" 

 set in upon these Woolwich beds as they trend westward from London. 



It has been shown in my previous papers that both the " Basement 

 Bed of the London Clay" and the "Thanet Sands" are respectively 

 nearly uniform in their lithological and palseontological characters 

 (when fossiliferous) throughout their entire range — the former being 

 coextensive with the London Clay itself, whilst the latter extend only 

 from the Isle of Thanet to a short distance westward of London — and 

 that both are essentially of marine origin. 



The middle division of the Lower Tertiaries, of which it now re- 

 mains to treat, is, on the contrary, in different areas so very different 

 in its lithological striicture and in its organic remains, that it presents 

 one of those cases where the evidence of supei-position is incUspensable. 

 Were it not for the well-marked horizons afforded by the upper and 

 lower divisions, which confine this group within distinct limits, it 

 would in fact often be difficult or rather impossible to identify its 

 synchronous beds, when viewed in detached sections, either by their 



* Organic Remains, vol.iii. p. 171, and Trans. Geol. Soc. 2nd ser. vol. iii. p. 212. 



t Trans. Geol. Soc. vol. ii. p. 196. J Ibid. vol. iv. p. 277. 



§ Geology of England, pp. 24-26 and 37-52. 



II Mag. Nat. Hist. June 1835, p. 356, and Proc. Geol. Soc. vol. ii. p. 450, 1837. 



** Proc. Geol. Soc. vol. i. p. 482 ; vol. ii. p. 551 ; vol. iii. p. 131. 



tt If/id. vol. ii. pp. 78, 222, 449 ; Trans. Geol. Soc. vol. vi. p. 211. 



+t Quart. Journ. Geol. Soc. vol. i. p. 172 ; Trans. Geol. Soc. 2nd ser. vol. i. p. 52. 



§§ Quart. Journ. Geol. Soc. vol. vi. p. 440. 



nil Sections of the London Strata. 



*** Bidletin, Soc. Geol. de France, 2nd ser. vol. ix. p. 350. 



