FOSSIL OYSTERS. 395 
- Monomyaria : Bivalve Shells, with one muscular impression. 
_ Ostrea, Lign. 120.—The Oyster is well known to possess 
no power of locomotion ; it is attached to rocks, pebbles, 
and other bodies, and forms extensive beds, consisting of 
- numerous individuals, of all sizes. There are many fossil 
_ species; the British strata yield between forty and fifty. In 
some localities, Oysters are found in thick beds, of great 
extent, apparently on the spots they occupied when living. 
One of the most interesting localities I am acquainted with, 
is Sundridge Park, near Bromley, in Kent, where a hard 
conglomerate, entirely made up of oyster-shells, and the 
shingle that formed their native bed, is quarried. This 
stone is much employed for ornamental rock-work, and 
several walls in and near Bromley are constructed of it : 
these display the fossils, some with the valves closed, others 
open, others detached, and the whole grouped as if artifi- 
cially imbedded to expose the characters of the shells. 
These oyster-beds belong to the tertiary strata of the London 
basin; they extend to Plumstead, and other places in the 
vicinity; and in some localities, the oysters are associated 
with other bivalves, called Pectwncult. In the tertiary clays 
near Woolwich and Bexley, fossil oyster-shells abound. In 
the neighbourhood of Reading, in Berkshire, an extensive 
layer of fossil oysters occupies the same geological position, 
namely, the lowermost sands and clays of the London basin. 
Wherever the strata around London are perforated to a suf- 
ficient depth, this oyster-bed is reached. Very recently an 
Artesian well was bored at Hanwell, in Middlesex, and at 
the depth of two hundred and eighty feet this stratum of 
sand with oyster-shells was found. At Headley, near 
Reigate, in Surrey, there is a similar deposit. These oysters 
very closely resemble the edible species. 
The White Chalk contains several species of Ostrea, but I 
believe no beds of these shells have been found in it; on the 
