26 GEOLOGY OF THE ISLE OF WIGHT. 



over the Wealden, or even in contact with it, it is not unreason- 

 able to suppose that the fish were killed by the change from fresh 

 water to sult.""^ Remains of fishes were identified by Sir Philip 

 Egerton, and a small Saurian phalanx by Professor Owen. 



The Perna Bed was so named by Dr. Fitton in consequence of 

 its containing great numbers of Perna Mulleti, Desh. (Fig. 8), 

 which has not been found in any of the other beds. Exogyra 

 (^Gryphcea) sinuata also occurs in abundance and of a large size. 

 The rest of the fossils will be found distinguished in the fossil 

 list on p. 261. 



The Atherfieltl Clay, which was also named by Dr. Fitton, is 

 of a pale-blue colour, and, unlike the Wealden Shales, is devoid 

 of lamination ; it contains numerous flat concretionary nodules. 

 " Among the fossils the most common in the lower portion is 

 Pinna rohinaldina, d'Orb. Ammonites are not unfrequent ; and 

 the remains of a turtle . . . were obtained here." (Fitton, 

 op. cit, p. 296.) The thickness of the Atherfield Glaj'- is about 

 60 feet, according to Fitton, but 99 feet according to Ibbetson 

 and Forbes, who include the Lower Lobster Bed in the sub- 

 division . 



The Lower Lobster Bed is an impure fuller's earth, abounding 

 in remains of Meyeria (Astacus), from which fossil it takes its 

 name. It is now grouped with the Atherfield Clay on purely 

 lithological grounds, the natural base of the ferruginous sands 

 which constitute the overlying group occurring above and not 

 below the Lower Lobster Bed. The thickness of the bed is 25 

 feet 6 inches according to Fitton, 29 feet according to Ibbetson 

 and Forbes. 



The Ferruginous Sands. 



This division of the Lower Greensand attains a thickness at 

 Atherfield of about 520 feet by Fitton's measurements, or 5u8 by 

 those of Ibbetson and Forbes. 



The lowest bed of the group, bed No. 5 of Fitton, and named 

 by him the Crackers, from the noise made by the waves in the 

 slight rocky prominence formed by the rock, consists of coarse 

 grey or brown sand, about 20 feet in total thickness. It contains 

 two layers of ferruginous and calcareous concretionary masses, 

 abounding in fossils. Some of the masses in the lower layer 

 "are 6 or 7 feet long, and a foot to 18 inches in thickness, and 

 almost composed of Gcrvillia ancejys (ariculoides), with Trigonia 

 dcedalea, Ammonites Desltayesii, fcc." (Fitton, oj). cit., p. 298.) 

 In the upper layer Dr. Fitton noted coniferous wood bored by 

 Teredo, and in the upjier part of the sand, TJietis, a large Astacus, 

 and Anunonitcs Deshaycsii. " In the lower part, great numbers 

 of Panopcea {Myacites) plicata, Sow., are found in it standing 



* (juart. .Jonrn. Gcol. Soc, vol. iii. p. 294 (1847). 



