356 Strata near Woolwich. 



Art. XII. Observations on the Strata near Woolwich. 

 By John Morris, Esq. 



The pit near the entrance of the town, which has so long 

 afforded the best section of the plastic sand formation of the 

 London basin, is so well known, that it would appear almost 

 useless to describe it again, had not some recent excavations 

 unfolded to us a few more facts concerning its organic con- 

 tents and physical structure. 



The following beds are displayed, in an ascending order, 

 about the middle of the pit : — Chalk, with flints, green sand 

 of the Reading oyster bed with flints ; 1 ft. Ash-coloured 

 sand, 35 ft. Greenish sand, with flint pebbles ; 8 ft. Iron- 

 shot coarse sand, without shells or pebbles ; 9 ft. Blue and 

 brown clay, containing O'strea, Cerithia, Cytheretf, Z?ucci- 

 num, &c. ; 6 ft. Brown and red clay, containing Cerithia, 

 Potamis, Cyrena, Melanopsis, &c. ; 6 ft. Small black flints 

 and sand, containing rolled fragments of Cerithium, Cyrena, 

 Melanopsis, Neritina, &c. ; 10 ft. Layers of large flints, with 

 various fossils of the chalk and green sand ; 2 ft. The fossil 

 shells of this deposit are chiefly to the blue and brown clays; 

 the marine shells, as O'strea, Cerithia, Zfticcinum, &c, pre- 

 dominating in the lower part ; and, though these occur again 

 in the brown clay above, they are mingled with evident fluvia- 

 tile shells, as Neritina, Potamis, Melanopsis, Cyrena *, &c. 

 Upon these clays rests an accumulation of sand and pebbles, 

 containing shells of the species found below ; but in a very 

 different state, being much worn and broken. Above this, 

 again, is a layer of larger flint pebbles, amongst which are 

 found various fossils of the green sand and chalk, as Am- 

 monltes, O'strea, Terebratulae, &c. 



As a connecting circumstance with this part of my subject, 

 I may mention that, at Bromley, in a similar stratum above 

 the pebbles and sand, there frequently occur fragments of 

 oysters, as well as perfectly rounded pieces of white chalk. 



If we now examine another section of the pit, which the 

 recent excavations have disclosed, a very different appearance 

 is presented, remarkable for the absence of that regular stra- 

 tification observed in the other portion ; beginning from the 

 west side, where there is an abrupt termination to the regular 



* These shells have generally been confounded with Cyclas, which are 

 stated to be found in this deposit : they, however, differ from them in 

 having the lateral teeth striated, which Cyclas has not, and are also much 

 stronger. Four species of Cyrena occur at Woolwich ; Cyrena obovata, 

 tellintiides, deperdita, and cuneiformis : the latter is particularly character- 

 ised by having the lateral teeth striated obliquely to the umbones. 



