102 i)r. J. W. Gregory — Fossils from the Lower Greensand. 



passage from the Folkestone Sands to the Gault, these three zones 

 must be represented by part of the former. Then the commencement 

 of the " epoch " of the Gault is represented not by the base of the 

 fossiliferous clays but by some part of unfossiliferous sands now 

 included in the Lower Greensand.^ 



This proposal is not altogether a new one, for the view was long 

 ago expressed that part, if not all, of the Folkestone Beds of Folke- 

 stone must be included with the Gaiilt. Thus Gaudry ^ advocated 

 this in 1860, and he has been followed by many Continental authors 

 and by Prof. Cole.^ This step has not, however, been generally 

 accepted, owing to the difficulty of separating the Ac. mammillare 

 zone from the rest of the Lower Greensand. Thus M. Barrois 

 maintains that we must include in the Gault, not only the Folkestone, 

 but also the Sandgate and Hythe Beds, owing to the unity of the 

 faunas of these three horizons ; and that as they contain the zone of 

 Ac. mammillare, they therefore belong to the Gault. He snys,* 

 " il est hors de doute que la partie superieure de ce Lower Green- 

 sand (Folkestone Beds) est notre zone de sables verts a Am. 



mammillaris ils [the fossils of this zone] sont tous du 



gault, et ce niveau ne pent etre separe du gault." And he proceeds : 

 "Si les Folkestone beds appartiennent au gault, les Sandgate beds, 

 Hythe beds, qui n'en different que d'une fagon insensible, devront 

 aussi appartenir au gault ; on ne pent songer a mettre une divisiott 

 d'etage au milieu du Lower greensand." 



Acanthoceras mammillare does not occur in the Lower Greensand 

 except in the uppermost of the four divisions into which Price has 

 divided the Folkestone Beds.^ This narrow zone must be included 

 in the Albian and regarded as part of the basement bed " of the 

 Gault; but only this. The three lower divisions of the Folkestone) 

 ]ieds and the Sandgate Beds, as well as the Hythe, are all below 

 the horizon of Acanth. mammillare and are therefore earlier than the 

 Albian. 



The following Table expresses the views here advocated of th© 

 relations of the Lower Greensand and Gault in Kent and Surrey : — 



This Table illustrates the differences between the formation scale 

 and the time scale. For the purposes of the map the separation of 

 the Gault and the Lower Greensand is of course necessary. But 



1 At a recent meeting of the Geological Society, Mr. T. Leighton announced 

 the discovery of a fossil in the Folkestone Sands. This is a cone which has been 

 identified by Mr. Carruthers as Pinites hexagonus, Carr. , (Geol. Mag. 1*<71, 

 Yol. VIII. pp. 040—544, PI. XV.), a species previously known from the Upper 

 Gault (zone ix.) of Eastware Bay. It is interesting to find that the only known 

 fossil from the Folkestone Sands inland is a Gault species. 



A. Gaudry, " Sur la decouvert de V Osto'aea Leymerii a Wissant (Pas-de- 

 ais)," Bull. Soc. geol. France, ser. 2, t. xvii. p. 32. 

 G. A. J. Cole, "Aids in Practical Geology," ed. 2, 1893, p. 387. 



* C. Barrois, " Sur le Gault et sur les couches eutre lesquelles il est compris dans 

 le bassin de Paris," Ann. Soc. geol. Nord. t. ii. 1875, p. 56. 



^ F. G. H. Price, " Onthe Lower Greensand and Gault of Folkestone," Proc. Geol. 

 Assoc, vol. iv. 1875, p. 139. 



^ The frequent "very decided passage from one to the other" {i.e. Folkestone 

 Beds to Gault) has been pointed out by Mr. Topley. " On the Lower Cretaceous 

 Beds of the Bas-Boulonnais." .Quart. Journ. Geol. Soc. vol. xxiv. 1868, p. 474. 



