164 NOTICES OF THE MEETINGS [April 2, 
WEEKLY EVENING MEETING, 
Friday, April 2. 
Sir Cuarues Fettows, in the Chair. 
Sir Cuarues LYELL, 
On the Blackheath Pebble-bed, and on Certain Phenomena in the 
Geology of the Neighbourhood of London. 
Tere are two kinds of flint-gravel used for making roads in the 
neighbourhood of London, both of them in certain places superficial, 
but which are of extremely different ages. The yellow gravel of 
Hyde Park and Kensington so often found covering the ‘‘ London 
Clay” may be taken as an example of one kind ; that of Blackheath, 
of the other. The first of these is, comparatively speaking, of very 
modern date, and consists of slightly rolled, and, for the most part, 
angular fragments, in which portions of the white opaque coating of 
the original chalk flint remains unremoved. The more ancient gravel 
consists of black and well-rounded pebbles, egg-shaped or spherical, 
of various sizes, exhibiting no vestige of the white coating of the ori- 
ginal flints, yet showing by the fossil sponges and shells contained in 
them that they are derived from the Chalk. In the pits of Black- 
heath and the neighbourhood, where this old shingle attains at some 
points a thickness of 50 feet, small pieces of white chalk sometimes 
occur, though very rarely intermixed with the pebbles. If we meet 
with thoroughly rounded flints in the more modern, or angular 
gravel, it is because the latter has been in part derived from the de- 
nudation of the older bed. 
The researches of the Rev. H. M. De la Condamine have shown 
that the sand and pebble-beds of Blackheath and Greenwich Park, 
inclose in some of their numerous layers, freshwater shells of extinct 
species, such as Cyrena cuneiformis, &c. agreeing with fossils which 
characterize the Lower Eocene beds at Woolwich. At Lewisham 
the pebble-bed passes under the London Clay, and at Shooter’s Hill 
this clay overlies it in great thickness. 
At New Charlton, in the suburbs of Woolwich, Mr. De la Conda- 
mine discovered a few years ago a layer of sand in the midst of the 
pebble-bed, where numerous individuals of the Cyrena tellinella 
were seen standing endwise, with both their valves united, the pos- 
terior extremity of each shell being uppermost, as would happen if 
the mollusks had died in their natural position. Sir Charles Lyell 
described a bank of sandy mud in the delta of the Alabama river at 
Mobile, on the borders of the Gulf of Mexico, where, in 1846, he 
had dug out, at low tide, specimens of a living species of Cyrena, 
and of a Gnathodon, which were similarly placed, with their shells 
erect, a position which enables the animal to protrude its siphons 
