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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 26, 



In tliat portion of the London tertiaries which Hes to the west of 

 London, one of the most characteristic features exhibited in the beds 

 immediately overlying the chalk, is the frequent occurrence of a band 

 of the Ostrea bellovacina, with a few sharks' teeth, imbedded usually in 

 a clayey greensand, and generally separated from the chalk only by a 

 bed, two or three feet thick, of greensand and clay, full of slightly- 

 rolled green-coated flints. Sometimes, however, the Ostrea band 

 descends to the chalk. 



These strata, with their associated mottled clays, are well known 

 from Dr. Buckland's description* of them at Katesgrove Pits, Reading, 

 whence westward they may be traced to the extremity of the London 

 tertiary district at almost all the points where these lowest strata are 

 exhibited. 



In the Hampshire basin this bed has not hitherto been known ; 

 but I had the satisfaction last summer of meeting with an excellent 

 exhibition of it in a cutting of the Southampton and Salisbury rail- 

 road at Kembridge, about three and a half miles north of Romsey. 



The agreement of this section with those exhibited in the neigh- 

 bourhood of Newbury and Hungerford is striking, and is not confined 

 to the layer of the Ostrea bellovacina, but extends to the associated 

 beds of mottled clays. At the south end of the cutting at Kembridge 

 the section is identical with that in immediate junction with the chalk 

 at Alum Bayf, both in the arrangement of the strata and in the ab- 

 sence of fossils ; but in proceeding northward, a band of oysters gra- 

 dually appears, and at the further end of the cutting attains a thick- 

 Fig. 1 . — Section on the Railway near Kembridge. 



a. Ochreous flint gravel. 



b. Red clays mottled with grey, dark pluni-colour, and yellow at its 



base. No fossils. (Identical with the mottled clays No. 2 of Alum 



Bay and of Reading.) 15 feet. 



c. Clayey yellow and greenish sand, with the usual layer of slightly- 



rolled, large green-coated flints at the bottom ; mixed also with a 

 few small round flint pebbles, and imbedded in an impure ochreous 

 and argillaceous greensand. Above the flints, and partly inter- 

 mingled with them, there is at the point "y" a layer about two feet 

 thick of large Ostrea bellovacina. Towards the south end of the 

 cutting it gradually thins out, and disappears altogether about 

 midway in the section. The shells of these oysters are mostly 

 very thick and large, and much corroded 4 feet. 



d. Chalk with flints. Its upper sm'face is rather uneven, and irregularly 



bored into from the greensand layer above, the substance of which 

 now fills the tubular holes. 



* Transactions of the Geological Society, 2nd series, vol. ii. part 1. p. 119. 

 t Excepting that the rolled flints on the chalk are at the latter place imbedded 

 in a rather whiter and purer sand. 



