Be Ranee — On the Albian, or Gault of Folkestone. 167 



not so dark as the zone of Jm. auritus var., and is highly 

 fossiliferous. Two distinct forms of Ammonites Deshayesii occur 

 in the lower Cretaceous series, one with a square flat back, the 

 other with a rounded back. The former occurs in the zone of 

 MhynchoneUa sulcata, and the sand seam in the zone of Am. in- 

 terruptus ; the latter form in the Lower Neocomian clay of the Isle 

 of Wight, and the clay of the Lower Albian, zone v., at Folkestone. 

 Zones v., vi., and vii. constitute the horizon of Ammonites elegans, 

 whilst that of Am. lautus probably corresponds with the entire space 

 occupied by the Lower Albian. 



Zone of Am. Beudantii. Bed. iv. being the ''passage" be- 

 tween the Upper and Lower Albian, cannot be strictly said to 

 belong to the one more than to the other. It marks the total extinc- 

 tion of many Lower Albian forms, no less than the introduction of 

 others, which took their place. But this replacement is marked rather 

 by a greater number of individuals, than of species, for of the 88 

 species which became extinct in the Lower Albian, only 45 new 

 forms occur as peculiar species to the Upper Albian. Zone iv., in 

 addition to being the "limit fauna" of the two Albians, contains 13 

 species peculiar to itself, and also the other 13 species which are com- 

 mon to the Upper and Lower Albians. We thus see how well the 

 Upper Albian is specialized by the group Cristati, not a single speci- 

 men of which is found in the Lower Albian ; whilst with the excep- 

 tion of Am. splendens, the Lower Albian is equally characterized by the 

 Dentati and Tuber culati — bed xi. being especially the zone of the 

 former, and beds vii., vi.,.and v. of the latter. This zone, as seen in 

 the patch on the beach, consists of four portions. The lower, five 

 inches at the outcrop, contain phosphatic nodules with Am. prohos- 

 eideus ; the second, 18 inches thick, nodules with variety of Am. 

 denarius [Am. crenatus of the Brit. Mus. coll.) ; the third, four feet 

 four inches, with few nodules and Am. Bouchardi ; the fourth, two 

 feet, with nodules and Am. Beudantii, constituting four well defined 

 Ammonitic horizons. 



UPPER ALBIAN. 



Zone of Nautilus Deslongchampsianus. Bed in. is at once 

 distinguishable from any other by the occurrence of Inoceramus 

 sulcatus, in casts, in great abundance, the surface of the bed being 

 everywhere marked by their silvery impressions. This shell first 

 occurs in the Lower Neocomian clay of Hythe, is not again found in 

 the Aptian series, but re-appears in the zone of ^m. interruptus\ a 

 single specimen only, however, has been found by Mr. Etheridge.^ 

 It next appears sparingly in bed iv., and reaches its maximum of 

 development in bed in., the zone under consideration. A few speci- 

 mens occur in bed ii., and also in the Blackdown beds, a portion 

 of which, at least, represents the Upper Albian. Near the base of 

 zone III. there is a seam of phosphate containing Nucula hivirgata and 

 Cardita tenuicosta, Inoceramus sulcatus^ and a quartz pebble. A little 



^ Memoir of the Geol. Survey, sheet iv. 



2 A distinct variety of In. sulcatus, figured in "Mollusques Fossiles," by Pictet 



