214 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



period anterior to any other of the French Tertiaries, and conse- 

 quently preceding the Glauconie inferieure. He regards them both 

 as formed in a large freshwater lake, the deposits of which were, 

 with the exception of a few isolated masses, swept away by an irrup- 

 tion of that sea in which the marine sands of Laon, Rheims, and 

 Beauvais were accumulated, and by which sands they are now, as it 

 were, incased. In a paper communicated last year to the Geological 

 Society of France, I have endeavoured to show that, on the con- 

 trary, these sands of Rilly are independent of the marls which overlie 

 them, that they contain marine shells, and that they are, in fact, 

 but part of the marine sands of Rheims and Laon which stretch 

 around them on the same level ; the difference of mineral character, 

 and the absence of shells, except as casts, being attributable to the 

 infiltration of limpid fresh water, charged with carbonic acid, which 

 deposited the overlying tufaceous marls or travertin*. 



Although on the whole we have not in England so full and varied 

 a development of organic remains in the Lower Tertiaries as prevails 

 in France, there are nevertheless some phsenomena, which I have 

 had occasion to observe in the Lower London Tertiaries, which may 

 tend to throw light upon these diiferences of opinion ; and, taken 

 together with the facts presented by the French series, may prove 

 sufficient to establish the order of superposition and the correlation 

 of the different beds. 



In England next above the Thanet Sands we have the complicated 

 series of Woolwich and Reading. In the Isle of Wight it consists 

 almost entirely of pure tenacious mottled clays, which range to the 

 neighbourhood of London ; but, as they approach this centre, they 

 become more and more interstratified with beds of sand and pebbles, 

 until at last these latter entirely replace the clays. With very few 

 exceptions the only fossil shell found westward of the vicinity of 

 London is the Ostrea Bellovacina, which occurs at places at the base 

 of the clays. In the neighbourhood of London, the Fluviatile beds 

 of Woolwich distinctly set in in the midst of this deposit with the 

 mottled clays both above and below them, and the whole mass be- 

 comes pervaded with a fluviatile and aestuarine fauna. Proceeding 

 further eastward these mineral characters undergo a further change ; 

 the clays die out, and, with the exception of occasional pebbly bands, 

 the strata pass into a mass of white and greenish quartzose sands ; 

 while at the same time the estuarine and fluviatile fauna gradually 

 disappears and is replaced by a marine one. It is, however, not until 

 we reach the N.E. of Kent that this change is effected ; and even 

 then the fossils are very rare, preserved as it were by accident, for 

 the calcareous matter of the shells has almost always been dissolved 

 out, and it is only in some few places, where siliceous casts have occu- 

 pied the produced cavities, that evidence of this marine fauna exists f. 

 (See PI. VIII., Diagram, str. a, e, andy.) 



* Bull. Soc. Geol. de France, 2nd Ser., vol. x. p. 300. M. Hebert has since 

 replied to these observations, and maintains his original views. He has also noted 

 some new localities, Bull. vol. x. p. 436. 



t For particulars of the changes in the structure and organic remains of this 

 series, see Quart, Journ. Geol. Soc, vol. x. p. 75-170. 



