NOTES AND QUERIES, 



413 



Coast Railway, near Brockley Lane, where earth has been thro\Mi up, and in it 

 are portions of shell-marl, containing Cenihinin, Ci/roia, with a few Faludhw, 

 and oysters. It is difficult to*obtain good specunens there, most being crushed, 

 opng to exposure to the weather.* Proceeding uoav in a north-westerly 

 direction over Telegraph Hill to witliin about a hundred and fifty yards south 

 of St. Mary's-church, Peckham, there is a small stream cutting through a shell- 

 bed, met with there in situ, fire feet six inches below the surface. Overlying is 

 •a band of pebbles about three inches in thickness, and above this a mass of 

 gravel and clay containing septaria and angular-flints. The marl here is so 

 destroyed by the action of running water as to render it almost impossilDle to 

 distinguish the species of the shells it contains; but in an adjoining field, where 

 excavations have been made for different purposes, the marl" has been thrown 

 up, so that with a little care and patience some tolerable specimens of Centhiiim, 

 Cijrena, and Fahid'uia can be obtained from the pieces scattered about. In 

 passing down the road towards the churcli we find on the left a pathway across 

 the fields, and after following it for a quarter of a mile, we come to a field on 

 the west side of the "Braid" and there find crushed shells of Ositrcca, Ci/reaa, 

 &c., scattered on the surface. Passing on to Cow-lane we discover near a 

 stream running for some distance by the side of the road a capital section, 

 sliowing distinctly the positions of the different strata : — 1st — a layer of oyster- 

 shells of about two inches ; 2nd — hard, compact shell-marl composed, of Cijroia, 

 anil Ceri.thiian, one foot three inclics ; 8rd — blue clay containing casts of Falii- 

 dim, many of which when broken present a very beautiful a])])earanee, closely 

 resembling the crystallization sometimes occurring in the Ciivities of hints, one 

 foot ; 1th — gravel with rounded pebbles, one foot six inches ; 5th — a mass of clay 

 four feet in thickness, containing septaria and a few flints. 



Now tlie oyster-bed (1) is evidently a contmuation of that wliich occurs at 

 Woolwich, though considerably tliinned out. The shell-marl (2) also seems 

 identical with that numbered 7 in the liev. Mr, Bonney's description ; but 

 the next (3) is decidedly a new bed not seen at AVoolwich, although it is found 

 at the church- and railway-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 

 mollusca, and the introduction of fresh-water shells. The shell-marl (2) which 

 is about fourteen feet thick at Woolwich here only reaches one foot three inches, 

 til inning out in its westward course ; while the overlying stratum, here twelve 

 inches, gradually diminishes eastwardly, until at Woolwich we find no traces of 

 it, although the pebble-bed there (6) may be of the same period, as I have found 

 in it some small Paludinai, which probably were washed down and killed by the 

 salt-water. 



We may conclude that the ocean once covered the site of the present oyster- 

 bed at the moutli 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 from the increase 

 of fresh-water deposited the overlying stratum, wliich naturally diminished in 

 thickness on the land-side, from the predominance inland of the river-water. 

 Still continuing to increase in volume, the next deposit of blue mud or clay 

 was formed containing the paludinse, 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 continuing to bring down mud and clay from the 



country which it drained again formed the deposits immediately above. During 



tt 



* At Eritli and some other places the shells, as found in sUn in the marl, are mnch crnshed 

 and broken.— Ed. Geol. 



VOL. II. 



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