244 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 25, 



The palaeontological changes exhibited in this series may have 

 taken place without any further change of level. The slightly 

 varying mineral composition, and the gradual change in the fauna, 

 result probably from the tranquil filling-up of the estuary and the 

 eventual barring-out of the salt water. 



With reference to the so-called upper marine formation, the strata 

 No. 56 to 61 in the Headon Hill, and No. 36 (which I consider its 

 equivalent) in the White Cliff Bay section, it overlies the preceding 

 group, from which it is not to be distinguished by stratification or 

 mineral character, except that it contains some small flint pebbles. 

 This however is a difference of some importance, as showing an in- 

 creased moving force of water, and it indicates therefore an influx 

 of the sea resulting probably from a slight further subsidence, 

 and again restoring for a time, as evidenced by the organic remains, 

 the conditions of the former estuary. The marine and estuary tes- 

 tacea, which had disappeared in the beds immediately preceding, 

 now re-appear in considerable abundance, accompanied by some 

 new species. 



At White Cliff Bay the change has not been so important as at 

 Headon Hill. At the former place one or two species of Ostrea, 

 wiih the Potamides cinctus, P. ventricosus, Melania fasciata, Cy- 

 rena obovata, C, cuneiformis, and Melanopsis are common. At the 

 latter place, however, a greater number of species occur, of which 

 the most characteristic are, in addition to those just mentioned, 

 Fusus labiatiis, Potamides acutus, Neritina concava^ a Cerithium 

 and a Natica identical with species from the calcaire grossier of Da- 

 mery, and probably also Ampullaria WiUemetii. 



At White Cliff Bay these beds pass upwards into thick strata of 

 green marls and clays, of which almost the only fossils are Paludina 

 lenta, Cyrena ohovata^ Melania fasciata , Melanopsis and Potamides. 

 This does not indicate so much of a freshwater condition as does 

 occasionally its equivalent at Headon Hill, which has been termed 

 the upper freshwater formation. As before observed, the estuary 

 fauna at No. 56 succeeds suddenly to the freshwater one, but in 

 ascending order the change is more gradual, several estuary species, 

 such as Melania fasciata, Melanopsis fusiformis, Potamides ventri- 

 cosus, and P. concavus, appearing in No. 61. No. 62 is a thin bed 

 full of Planorbis and LimncEa ; and in the thick mass of earthy lime- 

 stones marked Nos. 67 and 68, the several well-known species of 

 these genera abound, and are associated with some teeth of the 

 Palceotherium and bones of a Tortoise. 



Slight changes of subsidence have again modified the higher beds 

 to a small extent : — the upper part of the last stratum is partially a 

 conglomerate, and in the marls which succeed we find the Cyrena 

 obovata, and in stratum 70 Melania fasciata ; in 71 the Planorbis 

 and Limncea again appear ; in 72 bones of the Tortoise, with Palu- 

 dina lenta and Neritina concava ; in 73 Cyrena obovata ; and in the 

 bed No. 75 at the top of the series, and immediately underlying the 

 gravel and sand, we find, in a brown clay having traces of lignite, 

 Melania fasciata, Potamides cinctus, and Cyrena obovata, estuary 



