446 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 5, 



The pebbles in some places, where but little sand is present, are 

 spotted or pock-marked (if I may use the expression), perhaps by 

 the protection which where in contact they afford each, other from 

 the action of percolating water. At the points of contact they often 

 adhere to each other, their surfaces breaking away when separated. 

 Occasionally they are cemented together in a hard conglomerate. 

 The pebbles are often of such magnitude (from 4 to 6 inches dia- 

 meter) as to indicate rapid motion of the water, and are deposited at 

 a high angle, amounting in one spot to 25°*. On the other hand, 

 beds of fine "pea-gravel," sand, and even clay (as in the above-men- 

 tioned spot), indicate intervals of comparative tranquillity. It is 

 under such conditions that organic remains occur, as in the well-known 

 bed at New Charlton (which has replaced No. 5 — see fig. 2) con- 

 taining semi-fluviatile shells. Some of these are in one spot in the 

 position of living animals, the Ostrece adhering to the upper surface 

 of the pebbles, and the anterior slope of Cyrena tellinella being 

 uppermost. Among the pebbles near this are rolled fragments of 

 OstrecB. The following fossils occur : — 



*Melanopsis ancillaroides, Desk. 

 *Neritina pisiformis, Fer. 



Natica. 



Buccinura. 



Turritella ? 

 *Teeth of Lamna contortidens, Agass. 



*CyreDa cuneiforrais, Fer. 



tellinella, Fer. 



Pectunculus Plumsteadiensis, Sow. 



Ostrea flabellula, LamJc. 



(uncertain). 



*Cerithium crenulatura, Desh. 

 *Potamides variabilis, Desh. sp. 



* These occur in the beds previously described. 



Similar deposits appear in the vale north of Shooter's Hill, oppo- 

 site Sir Edward Pellatt's Gate, on Blackheath east of the south en- 

 trance to Greenwich Park (see fig. 3), and on Plumstead Common. 



Fig. 3. — Section in a Pit on the South side of Greenwich Park. 



(30 feet by l6 feet.) 



8 : , 



1, 5 & 7. Pebble bed (No. 6) in its ordinary condition. 



2, Bed of pebbles, with shells in the darker part. 



3. Grey laminated sandy loam. 



4. Irregular indistinct line of brown sand. 



6. Reddish mottled loam with a peciiliar saline taste. 

 8. Alluvium. 



From this pebble-bed much of the more recent gravel in the neigh- 

 bourhood has been derived, but the latter may always be distinguished 



* The dip of this 

 the compass. 



false stratification " varies on Blackheath to every point of 



