1850.] 



PRESTWICH ON THE LOWER TERTIARY STRATA. 



263 



Organic remains of stratum "c," at Maryland Point. 



Cardium Plumsteadiense, Sow. 

 Cytherea obliqua, Desk. 

 Calyptrsea trochiformis, LamJc. 

 Fusus. 



Melania inqninata, Defr. 

 Natica glaucinoides, Sow. 

 Ostrea Bellovacina, Lam. 

 Pectunculus brevirostris, Sow. 



Pectunciilus Plumsteadiensis, Sow. 

 Pleurotoma, a small ribbed species. 

 Rostellaria Sowerbvi, Mant. 

 Tellina ? 

 Scalaria. 



Teeth of Lainnse. 



A boring MoUusk, probably a Litho- 

 domus. 



It will be observed that this bed is here as well characterized as at 

 Clarendon Hill or Chinham, and that, with the exception of a single 

 specimen of the Melania inquinata, its fauna does not at all resemble 

 that of the Woolwich fluviatile beds. This solitary specimen had 

 also the appearance of having been rolled and worn. 



The low country along which this bed outcrops from Stratford to 

 Horndon is covered with gravel and exhibits no sections. Some years 

 since, however, a group of shells, similar to the above, was found 

 at Stifford Bridge near Purfleet, and specimens of them are, I am in- 

 formed by Mr. Morris, now in the Geological Museum at Cambridge. 



On the south side of the Thames, another outlier of the London 

 clay exists, I believe, on the Swanscombe Hills near Greenhithe, but 

 although I have examined them closely, I have not been able to meet 

 with a section of the basement beds. 



We next arrive at the fine sections at Upnor on the banks of the 

 Medway two miles north of Rochester. We there have nearly all 

 the beds between the London clay and the chalk exposed in a few 

 large sections. For the present it will be sufficient to exhibit the 

 upper part of the section on the banks of the Medway, a short 

 distance beyond the Castle*. (See fig. 10.) 



10. — Section at Upnor. 



London clay ; upper part dark brown and very tenacious, pass- 

 ing down into sandy lighter coloured beds. No organic re- 

 mains have been yet found in it. 



Brown clay and ochreous sand, with traces of lignite. 

 2. Light greenish sand, with a few patches of friable 

 shells. 3. Fine yellow sand, with a few shells. 4. In- 

 durated clay, with numerous shells and traces of 

 plants. 5. Yellow sand, the upper part full of round 

 flint pebbles, and the lower part abounding in shells. 

 Concreted masses, full of shells, not uncommon. 



1. Light yellow and whitish sand ; upper surface indented 

 by stratum "c;" contains a few shells {Ostrea and 

 Cyrena) in irregular patches, and occasionally an un- 

 derlayer of large Ostrete. 2. A series of dark tough clays, 

 with subordinate lignite and beds full of the fluviatile 

 shells of Woolwich. 3. Variable yellow sands, reaching 

 probably to the chalk, at a depth of 50 or 6o feet below 

 "c." 



* This section is described by Mr. Morris in the Proc. Geol. Soc. vol. ii. p. 451, 



