iSTfeATA IN THE NEICHiOUttHOOD OF LONDOif. 113 



The pehb'es are almost all of a roundish oval form, many pebbles. 

 of them being striped, but differing from those of the supe- 

 rior 'ti^tom, in being seldom broken, in there being few 

 larjje ramose masses, and in their not bearing any marks or 

 traces of organization* Many of these pebbles are passing i <^ 



into a slate of decomposition, whence they have in some 

 degree the appearance of having been subjected to the action 

 of fire: small fragments of shells are every where dispersed 

 amongst them. 



Beneath the pebbles is a stratum of light fawn coloured Sand bcneam 

 «and of about ten feet in depth, and immediately under this ^ ®*®* 

 is the stratum of white sand, which is about five and thirty 

 feet deep, and is here seen resting immediately on the 

 chalk. 



At Plumstead, about a mile distant in a south-eastern di- Shells at 

 rection, there is a pit in which the shells, about two years ^^l^n^stoa*^ 

 ago, were to be obtained in a much better state of preservation 

 than at New Charlton; but this seam of shells, as the pit 

 has been dug farther in, has by degrees become so narrow, 

 as to be now nearly lost. In this pit, not only the shell* 

 already mentioned were found, but many tolerably perfect 

 specimens of calyptnta trochiformis , Lam., trochus aperttrSf 

 Brander., arcee glycemeres, arcce Naticce, and many minute 

 shells in good pretecrvation. All these shells appear to have 

 entirely lost their anirnal matter, and, not having become 

 imbued with any connecting impregnation, they are ex- 

 tremely brittle. On examination with a lens it also appears, 

 that in most of the specimens nothing of their original surface 

 remains, it having been every where indented with im- 

 pressions of the surrounding minute sand, made while the 

 shells were in a softened state. This circumstance is parti- farticular cha. 

 cularly evinced in the cyclades, in which a particular charaC- ^jngg '"f ^on« 

 terinthe hinge was thus concealed; in a mass of these shells concealed. 

 from the Isle of Wight, it appears, that the lateral teeth are 

 icrenulated, somewhat similar to those of t\\e mactra solida 

 iu the gravel stratum; but in the cyclades o{ Plumstead, 

 this was not discoverable from the injuries, which their sur- 

 face had sustained from the sand. 



The fossils of this stratum evidently agree with those found "^^^^ same fo»« 

 by Lamarck and Mr. De France, above the chalk at Grignon, France, ar.d in 

 Vol. XXXI.— Feb. 181?. I O.urtagnon, 



