LOWER GREENSAND. 49 



" 111 the midst of this epoch of Gryphcea there is a sudden 

 reappearance of the muddy deposits, during the predominance of 

 which those animals adapted for such a sea-bottom, and which 

 had survived the deposition of the fullers' earth, again multiplied, 

 but the species which had become extinguished were not replaced 

 by representative forms. This, however, did not last long, the 

 sand again predominating with its zones of Gryplicea and lines of 

 Crioceras nodules. 



" A temporary multiplication of Terehratula sella suddenly 

 marks a change in the zoological conditions, — for the Cejihalopoda 

 disappear, although the zones of Gryph(Ba, which animal does not 

 appear to have been affected by the change, (probably a change in 

 the depth of the sea,) go on as before, there being, however, no 

 alternating lines of nodules. It would seem that the sea began to 

 shallow, probably from elevation of the sea-bottom, until at last 

 the Gryplicea itself disappears, the bands exhibit traces of the 

 influence of currents, and become more gravelly ; lignites, indica- 

 ting a shallow sea, become common, form belts in the ferruginous 

 sand, and in one place a bed in the wavy blue sand, at a time 

 when much iron was deposited. I^'he deposition of the peroxide of 

 iron appears to have been connected with the disappearance of the 

 majority of mollusca, though Trigonia, Thetis, and Venus occa- 

 sionally occur in considerable numbers. In the uppermost strata 

 scarcely any animal remains are found, and everything appears to 

 indicate a barren and shallow sea, previous to a new state of 

 things, when a fresh series of clays (forming the Gault) being 

 deposited, the majority of the animal forms which characterise the 

 clays of the Lower Greensand disappear, and are replaced by 

 distinct species, representative in time." 



Correlation with the Mainland and the Continent. 



Dr. Fitton first pointed out the identity of the fossils in the 

 Atherfield Clay of the Isle of Wight with those of a clay in 

 Sussex and Kent,* which corresponded to the Atherfield Clay, 

 except in the absence of the fossiliferous stone known in the Isle 

 of Wight as the Perna Bed. The calcareous nodides of the 

 '■ Crackers Eock " were considered by him to represent the 

 thick limestone (Kentish Kag) of Hythe, Maidstone, &c. The 

 Carstone and Sand-rock Beds of the present Memoir were identi- 

 fied by him as the upper division of the Lower Greensand which 

 he had described at Folkestone, that is to say, the Folkestone 

 Beds of the Geological Survey ; while the great mass of beds 

 intervening between the Sand-rock Series and the Crackers 

 group were correlated with his middle division at Folkestone, 

 now known as the Sandgate Beds. Lastly, he noticed that 

 the Ferruginous Beds of Blackgang Chine (Group XIV.) and the 

 corresponding bed of Horseledge, near Shanklin, contain the 

 same species as are found in the Sandgate Beds at Parham Park 



* Proc. Geol. Soc, vol. iv. pp. 198, 208, and 396 (1843). 

 E 56786. D 



