444 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [JuilG 5, 



At Charlton this bed contains a Httle selenite, large crystals of 

 which were also met with in a well sunk on the east side of Black- 

 heath. In the Blackheath cutting a large quantity of pyritous lignite 

 was found in one of the hollows worn in the surface of No. 2 before 

 the deposition of this bed. The thickness of this bed varies from six 

 to twenty feet. It is worked for bricks between Plumstead and 

 Woolwich. 



No. 4, the Shell-bed, is the great deposit of organic remains of this 

 formation. Its appearance and contents at Woolwich and Charlton 

 are well known. It is also well developed at Deptford, where the 

 lower part is blue and argillaceous, the upper yellow and sandy. In 

 the former, the interstices between the Ostreca are often filled with 

 yellow calcareous spar. The upper part contains the best-preserved 

 fossils, the sandy matrix having protected even the ligament * of the 

 Cyrence, and the coloured markings of the shells being occasionally 

 preserved in the more compact and stony layers. Rolled pebbles are 

 here mixed with the shells, together with fragments of vegetable 

 matter. 



At Loam-pit Hill this bed appears as a chocolate-coloured mass of 

 crushed shells, with a layer of Ostrece, Cerithia, and Cyrence imper- 

 fectly preserved. 



At Lee it is a hard limestone (known to well-diggers as " the 

 cockle"), capped with a layer of crushed shells, which in Blackheath 

 Park resembles ill-mixed mortar. 



At Morden College it expands to the thickness of eight feet, con- 

 sisting of blue shelly clay, with a few stripes of sand containing as 

 usual the most perfect shells. The Cyrence are often filled or lined 

 with sparkling pyrites. The Cerithia appear to affect the neigh- 

 bourhood of the Ostrece, as if the former had been rolled along by a 

 current until they stopped against the larger shells. The existence 

 of such a current is attested by the rolled pebbles in this bed at 

 Deptford. 



In the late Sir W. Gosset's grounds at Charlton, this bed consists 

 entirely of broken Ostrece resting on the very irregular surface of the 

 bed No. 3. It thins out and disappears east of Plumstead. 



I have procured the following fossils from this bed f : — 



Cyrena Gravesii, DesJi. *Melania inquinata, Defr. (4 van) 



* cuneiformis, Per. Rostellaria. 



■ trigonula, Wood. *Cerithium crenatulatam, Desk. 



(uncertain, intermediate in cha- *Potamides variabilis, Desk. sp. 



racter between the last two). *Melanopsis ancillaroides, Desk. 



Ostrea pulchra. Sow. *Rissoa, and a few uncertain species. 



* edulina, Sow. *Wood. 



* These occur in " No. 5." 



No. 5 is a distinctly stratified bed of yellow sand and loam, the 

 latter sometimes lead-coloured; the stratification is often marked 

 by thin laminae of clay. It abounds in concretions, pyritous at 



* The microscope has shown that the animal matter in these ligaments has 

 been beautifully and exactly replaced by carbonate of lime, 

 t I am indebted to Prof. E. Forbes for most of the names. 



