NOTES AND QUERIES. 
413 
Coast Railway, near Brockley Lane, where earth has been thrown np, and in it 
arc portions of shell-marl, contaiiiiug Cerithinm, Ci/reiia, with a few Pali(dhup, 
and oysters. It is difficidt to obtain good specimens tlicre, most being crushed, 
owing to exposure to the weather.* Proceeding now in a nortli-wcstcrly 
direction over Telegrapli Hill to within about a hundred and fifty yards south 
of St. Mary's-church, Peckham, tliere is a small stream cutthig through a sliell- 
bed, met with there in situ, five feet six inciies below the surface. Overlying is 
a band of pebbles about three inches in tliickness, and above this a mass of 
gravel and clay containing scptaria and angular-flints. The marl here is so 
destroyed by the action of running water as to render it almost impossible to 
distinguish the species of tlie shells it contains ; but in an adjoining field, wlierc 
excavations liave been made for different purposes, the marl has been thrown 
up, so that with a little care and patience some tolerable specimens of Ceritliiinii, 
Ci/rena, and Paliidiita can be obtained from tlie pieces scattered about. In 
passing do^vu the road towards the cliureh we find on tlie left a pathway across 
the fields, and after following it for a quarter of a mile, we come to a field on 
tlie west side of the " Braid" and there find crushed" shells of Odnca, Cyreiia, 
&c., scattered on the surface. Passing on to Cow-lane we discover near a 
stream running for some distance by tlie side of the road a capital section, 
showing distinctly the positions of the different strata: — 1st — a layer of oyster- 
shells of about two inches ; 2nd — hard, compact shell-marl composed, of Cj/rena, 
and Cerit Ilium, one foot three inches ; 3rd — blue clay containing casts of Palu- 
di/ia, many of which when broken present a very beautiful appearance, closely 
resembling the crystallization sometimes occurring hi the cavities of flints, one 
foot ; 4th — gravel with rounded pebbles, one foot six inches ; 5th — a mass of clay 
four feet in thickness, containing scptaria and a few flints. 
Now the oyster-bed (1) is evidently a contmuation of that which occurs at 
Woolwich, though considerably thinned out. The shell-marl (2) also seems 
identical with that numbered 7 in the llev. Mr. Bonney's description ; but 
the next (3) is decidedly a new bed not seen at Woolwich, although it is found 
at the church- and raU way-cuttings, a few inches in thickness. The pebble-bed 
(4) seems contemporaneous with No. 4 in the Woolwich section, but appears 
destitute of fossils. 
It is interesting to mark the gradual diminution of the salt and brackish 
moUusca, and the introduction of fresh-water shells. The shell-marl (2) which 
is about fourteen feet thick at Woolwich here oidy rerclies one foot three inches, 
thinning out in its westward course ; while the overlying stratum, here twelve 
inches, gradually diminishes eastwardly, uutil at Woolwich we find no traces of 
it, although the pebble-bed there (G) may be of the same period, as I have found 
in it some small Paludiuge, which probably were washed down and kUled by the 
salt-water. 
We may conclude that the ocean once covered the site of the present oyster- 
bed at the mouth of a large river which seemingly followed nearly the same 
course as the Thames at the present time. 
The salt-water gradually receding or becoming brackish fi-om tlie increase 
of fresh-water deposited the overlying stratum, which naturally diminished in 
thickness on the land-side, from the predominance inland of the river-water. 
Still continuuig to increase in volume, the next deposit of Idue mud or clay 
was formed containing the paludina?, so characteristic of its fresh-water 
conditions. This bed thins out, as we should have expected, in an opposite di- 
rection. The old river still contmuing to bring down mud and clay from the 
country which it drained again formed the deposits immediately abo^ e. During 
' At Erith and some othei' places the shells, as found in siVw in the marl, are mnch crushed 
and broken.— Ed. Geol. 
VOL. II. 
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