102 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



This distinguishing feature is, however, so irregularly maintained, 

 that at Erith, where in the Ballast pit this middle group overlies the 

 Thanet Sands, the line of demarcation between them can hardly be 

 traced : the two sands are almost exactly alike, and the pebble seams 

 are wanting. But the organic remains here assist us, as a band, 

 marked by the occurrence of the Ostrea Bellovacina, defines the line 

 of separation of the two groups*. 



Above this basement-bed are a series of fluviatile clays and pebbly 

 sands generally abounding in fossils. It is in the lower part of this, 

 or in the middle of the central division of the Lower Tertiaries, that 

 the well-known fluviatile clays of Woolwich are placed. This stratum 

 ranges from Londonf to Rochester, a distance of thirty miles, but 

 with a breadth not exceeding five to six miles, except near London, 

 where it extends from twelve to fifteen miles. The general character 

 of this bed is well knovni from the descriptions of Dr. Buckland, 

 Dr. Mitchell, Mr. Morris, and the Rev. H. De la Condamine, to 

 whose papers I beg to refer J for some of the principal sections in 

 this district. 



As, however, the fossils of the Woolwich pits require both additions 

 and corrections, I herewith annex a list of those found in the bed of 

 dark grey clay (Nos. 7 & 8 of Dr. Buckland). 



Organic Remains of the Woolwich Clay Bed, Ballast Pit § . 

 (PI. I. Diag. k, Loc. sect. 25.) 



Cyrena cuneiformis, Fer. Nucula fragilis, Desk. 



deperdita, Sow. Ostrea Bellovacina, Desk. 



cordata, Mor. tenera, Sow. 



Cerithium variabile, Desk. Hydrobia Parkinsoni, Mor. 



gracile, Mor. Planorbis hemistoma, Soiv. 



Cypris ? Psammobia Condaiuini, Mor. ? 



Fusus latus, Sow. Small Corallines. 



Melania inquinata, Desh. Opercula (of Cerithium ?). 



Melanopsis buccinoides, Fer. Eggs of Molluscs ? 

 Neritina globulus, Bef. 



The fossiliferous pebbly sands overlying this clay bed at the 

 Woolwich pit must, I think, be referred to the upper part of this 

 series. They contain the following fossUs : — 



Organic Remains of the Pebbly Sands, Woolwich Ballast Pit. 



Area depressa, Sow. Buccinum (Pseudoliva) fissuratuni, 



Auricula pygmsea, ATor. Desh. 



Balanus ? Calyptrsea trocbiformis, Lam. 



* See also Journ. Geol. Soc. vol. vi. p. 443. 



f Including the detached and isolated patch (which however belongs to a 

 higher part of the series) at Guildford, the range of the flm-iatile beds would be 

 nearly sixty miles. 



J Jnte, p. 76. 



§ The fossils of tliis pit have been most carefully worked out by Mr. De la 

 Condamine, Mr. Lunn, and Mr. Rosser, in whose collections I found most of the 

 rarer specimens of the accompanying lists. 



