116 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



eaten surface full of the small holes made by some minute boring 

 sponge. 



The surface of the chalk beneath the Oyster-bed is frequently 

 perforated with numerous irregular tubes, running about 6 inches to 

 a foot perpendicularly into the chalk, and filled with green sand from 

 the superincumbent bed. This is particularly visible at Kembridge, 

 Clay Hill, near Newbury, and at Reading. 



The shells in this area are found in all stages of growth ; many 

 attain a large size. Some of the Ostrea Bellovacina measure 5 or 6 

 inches by 4 and 5 ; the Pectunciihis 1^ to If inch in both direc- 

 tions ; the Crjrena deperdita and cordata have a breadth of \\ inch ; 

 and the C. cimeiformis sometimes as much as 2 inches ; whilst the 

 Mela?iia inquinata is often 2\ to 2f inches long, the Cerithium 

 variabile nearly 2 inches, and the Melanopsis i^j to 1^ inch. 



The brown epidermis of some specimens of Cyrena can sometimes 

 be distinctly traced, and the ligament occasionally remains. Some- 

 times even the colouring of the shells has not entirely disappeared, 

 and the fine marking on some of the small Neritince is often retained. 

 The dried animal matter of the animal itself is sometimes preserved 

 in small brown pieces in the interior of some of the shells. Some 

 of the small seed-vessels and portions of leaves also occasionally 

 retain their elasticity and traces of their brown colouring matter. 



In the few pits between Upnor and Boughton, which exhibit 

 sections of the lower part only of the " Woolwich and Reading series," 

 I have not, any more than in the same beds at Upnor, been able to 

 discover organic remains. At Boughton, where there is a change 

 hi the lithological structure of the Woolwich beds, it is accompa- 

 nied at the same time by a complete alteration in the organic remains. 

 All traces of the fluviatile shells of Woolwich are lost, and the equi- 

 valent beds, which are however imperfectly exposed, appear here to 

 be unfossiliferous ; but the light greenish sands on the level of the 

 pebbly green sands and Ostrea Bellovacina beds of the central and 

 western areas contain, with a few of the Woolwich forms, a new 

 group of marine fossils in the state of fine siliceous casts. Several 

 of the shells found here, such as the Cucidlcea crassatina, Cytherea 

 Bellovacina, and Corbida (Arnouldi ?), are common to the imder- 

 lying Thanet Sands ; but there are others which are peculiar to these 

 overlying beds, such as the fine Cyprina Scutellaria, the Pectunculus 

 terebratnlaris, the Cardium Plumsteadiense, and the Corbula Re- 

 gidbiensis. 



In the neighbourhood of Canterbuiy this division is unfossihferous, 

 but in the clifiFs between Heme Bay and the Reculvers we again 

 meet with the zone of silicified fossils {ante, p. 1 11). 



Nearer the Reculvers these beds contain silicified wood, of which, 

 however, better specimens have been found by the Rev. James Lay- 

 ton of Sandwich in the pits between Ash and Yrodnesborough. The 

 structure of this wood is in general coniferous, but some specimens 

 show a remarkable form of dicotyledonous texture. No shells are 

 found there. At Richborough the lower part of this group again 

 presents a thin band of silicified fossils of the same species as those 



