158 GEOLOGY OF THE ISLE OF WIGHT. 



of green sand ; the whole comprising a thickness 

 of between 200 and 300 feet. In some of these 

 deposits, the usual London clay shells are abun- 

 dant, especially near the spot marked c, in lign. 

 11.* The dark sandy clay immediately on the 

 north side of the chasm b, is also very prolific, 

 and I have collected from it numerous choice 

 specimens ; nummulites, and other foraminifera, 

 occur in some of the beds.-j- 



We now arrive at the foot of Headon Hill ; and 

 here the lowermost stratum visible on the beach 

 is a pure white sand, which is largely exported 

 for the glass manufactories ; this is covered by 

 a bed of yellowish clay. A series of variously 

 coloured sands, marls, and clays, with layers of 

 friable limestone succeed. The predominating 

 fossils are species of the freshwater genera, limneus, 

 planorbis, melanopsis, potamides, cyrena, Sec, with 

 which the reader is already familiar. But there 

 are in some of the beds a lew marine and estuary 

 shells, as cytherea, ancUlaria, corbida, &c. ; and 

 a layer of oyster shells occurs, similar to that 

 already noticed in the cliff in Colwell Bay. 

 Within 50 feet of the top of the hill, there is 



* The two figures in the fore-round, PL IX., are near this locality. 

 t See Mr. Prcstwich's " Memoir," for lists of the characteristic fossils 

 found in each stratum, throughout the entire series of deposits. 



