PRESTWICH WOOLWICH AND READING SERIES. 131 



20 feet of pebbly light greenish sands overlying the Thanet Sands 

 in West Kent, consist of a clear sharp quartzose sand mixed more or 

 less with grains of green sand, flint pebbles, and argillaceous matter. 

 Now, although the latter are almost always present, still the pro- 

 portion of them becomes in places so small that their presence is not 

 readily apparent, and a bed of sand, more or less pure and white, 

 remains. The great development of pebbles in this bed takes place 

 in the neighbourhood of London. As the beds range eastward they 

 pass into sands, often apparently forming with the " Thanet Sands " 

 one nearly undistinguishable mass ; and in the same way as they range 

 westward they occasionally put on, from this loss of the pebbles and 

 green grains, almost exactly the characters presented by the Thanet 

 Sands at Woolwich and Lewisham, and for which they have hitherto 

 been mistaken. Still, on the whole, the presence at the base of the 

 Woolwich and Reading series of slightly argillaceous sands, more 

 or less mixed with green sand and flint pebbles, is a most per- 

 manent lithological character of this division. We have, further, 

 some evidence, scanty though it is, of organic remains, the Ostrea 

 Bellovacina and teeth oiLamna occurring at intervals at the base of 

 the iBottled-clay series of Reading, from Huugerford and Newbury 

 to Headley, Hanwell, Northaw, and Hertford, and again beneath 

 London (sections in Appendix), where the mottled clays of Reading 

 become intercalated with the fossiliferous beds of Woolvdch ; and 

 further eastward in the same position at the base of this series 

 at Erith, where the Woolwich type alone obtains. This organic link 

 does not extend further eastward, unless the Ostrea at Oakwell 

 should, when better specimens are obtained, prove to belong to that 

 species ; but the teeth of Lamna are, however, met with. Under 

 ordinary circumstances but little weight could be attached to the 

 evidence of two such fossils, or of such common mineral characters ; 

 still, when we take into consideration the chances of their associa- 

 tion, their conjoint evidence becomes of much greater value, although 

 after all the aid of superposition is necessary. On these data 

 taken together, the pebbly sands, with their zone of 0. Bellovacina, 

 may be considered as a sufficiently definite anJ well-marked horizon 

 between the Woolwich and Reading series and the Thanet Sands. 

 In the neighbourhood of London this lowest bed of the Woolwich 

 series further shows, by the occasional presence of the Cyrena cunei- 

 formis, Melania inquinata, and Cerithium variahile, a fauna distinct 

 from that of the Thanet Sands ; but in East Kent, where the change 

 of condition between the two periods is not so marked, part of the 

 marine fauna of the latter is continued upwards into the former 

 deposit, many species of which may be particularly sjjecified, the 

 Cucullcea crassatina, Sanguinolaria Edwardsii, Corhnla Iteyulbiensis, 

 Ci/priiia Morrmi, Thracia oblata, Cyfherea Bellovachia, Jiinrullana. 

 suhdepressu, and Ghjcimeris Rutii-pieiisis, passing from the Thanet 

 Sands into the Woolwich series. Other spcci<'s, however, as the 

 Puuopcea (jranulata, Fecleu Prestvichil, Pholaduinya cuncata and 

 Koninckii, Sculuria Bowcrbaakii, Troplioii tmb nodosum, and Leda 

 substriata, do nut extend higher than the "Thanet Sands," whilst 



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