PRFSTWICH — WOOLWICH AND READING SERIES. 113^ 



Arapullaria subdepressa, Mor. Cyprina Morrisii, Sow. 



Cardium Plumsteadiense, Soiv. Cytherea Bellovacina, Desk. 



Laytoni, Mor. Dentalium. 



Corbula Regulbiensis, Mor. Glycimeris Rutupiensis, Mor. 



Cucullaea crassatina, Lam. Pectuuculus terebratularis, Desk. 



Cyprina Scutellaria, Desk. Sanguiiiolaria Edwardsii, Mor. 



All these species are silicified, and many of them in the most per- 

 fect and delicate state of preservation. (For the description of this 

 section see Journ. Geol. Soc. vol. viii. p. 251 and pi. 15.) 



On Woodnesborough Hill and at Ash the Woolwich sands are 26 

 to 30 feet thick, and consist entirely of one mass, nearly uniform 

 throughout, of light-coloured quartzose sands with green sand in dis- 

 seminated grains and patches, and with a few dispersed pebbles and 

 slight ochreous patches and concretions. No shells have been found 

 at these latter places, but Mr. Layton has procured from several pits 

 in that district, especially the one at Marshborough, a number of spe- 

 cimens of silicified wood with the structure beautifully preserved. 

 Some of them are pierced by the Teredo, which in one specimen is 

 quite in its young state, just adhering to the wood. These specimens 

 appear identical with those found in these beds at the Reculvers. 



I have not met with any beds of the Woolwich group in the Isle 

 of Thanet. 



§ 3. Organic Remains. 



As local lists of the organic remains have been given in the pre- 

 ceding pages, it now only remains to consider their general distribu- 

 tion, association, and condition, and to tabulate the whole. 



It has been shown that the Woolwich and Reading series, far from 

 being characterized throughout by similar fossils, exhibit peculiar 

 assemblages in different districts. Where the mottled clays prevail, 

 as over the greater part of the Hampshire and throughout all the 

 London district west of London, organic remains seem altogether 

 wanting, with the exception of the irregularly distributed layer of 

 the " Ostrea Bellovacina " at the base of this group, and of the local 

 plant remains at Reading, a few feet higher in the series, but still 

 near its base. 



The Woolwich beds continue comparatively barren until they 

 reach the neighbourhood of London. Concomitant with the litholo- 

 gical change before-described, the peculiar group of fresh and brackish 

 water shells of Woolwich appear, and attain their maximum develop- 

 ment at London, New Cross, Deptford, Woolwich, Bromley, Chisel- 

 hurst, and then decrease in variety and abundance as the beds range 

 to Rochester and Upnor. The species are not many, but the indi- 

 viduals of several are very numerous. 



The more strongly marked freshwater conditions are confined to 

 nearly the upper portion of this series at New Cross and a short 

 distance around, where the U7iio, the Paludina, the small Hydrobia 

 Parkinsoni, and the Melanopsis buccinoides are abundant. The sands, 

 pebbles, and clays just beneath the above contain a more mixed group, 

 of which the prevailing species are the Cerithium variabile, Melania 



VOL. X. PART I. I 



