240 



ME. W. HILL ON THE BEDS BETWEEN THE 



Ohallc with many Micrasters. — Almost immediately above the 

 flint line which I take as the upper limit of the zone of Holaster 

 jplanus^ the chalk, from being comparatively unfossiliferous, be- 

 comes crowded with organic remains. This division (see fig. 2), 

 which may be said to include all the "■ Nodular Chalk of Dover " — 

 the t" Chalk with [many:|:] organic remains" of W. Phillips — is 

 distinguished by the abundance of Micrasters. Its thickness at 

 the eastern end of the town of Dover is, as before stated, 81| feet. 



Zone of Micraster breviporus. — The basal portion of this division 

 is marked by the abundance of Micraster hreviioorus. Holaster 

 planus occurs rarely. Although this zone might be taken as an 

 extension of the zone of E. planus §, from the occurrence of this 

 fossil, yet, from the lithological character of the chalk, from the 

 presence of many Micrasters., and also because the fossils of the 

 appended list were to be found as generally in the zone above as in 

 this one, it appears to me to belong to the overlying rather than to 

 the underlying chalk. It is difficult to give the upper limit of this 

 zone ; but the abundance of Micraster breviporus seemed to warrant 

 the separation of the lower 15 feet of this division. Among the 

 many forms which are common at this horizon, are several species 

 of Gasteropods ; these may be found up to the band of hard yellow 

 rock in the overlying zone, beyond which they do not occur or are 

 rare. 



Zone of Micraster cor-testudinarium.- — Throughout the remainder 

 of this division Micraster cor-testudinarium is common ; other fossils 

 are abundant in the lower part of this zone, but as the hard yellow 

 rock passes into the soft white chalk with regular lines of flints, they 

 gradually become less plentiful and the chalk again comparatively 

 unfossiliferous. I do not fix the upper limit of this zone, but 

 M. cor-testudinarium was to be found commonly where the upper 

 part of this rocky nodular chalk descends to the beach at St. Mar- 

 garet's Bay. 



List of Fossils from the Challc luitJi many Micrasters ( = the Nodular 

 "^Z^,, ChalJc of Dover). — Zones o/ Micraster breviporus and Micraster 

 cor-testudinarium. (The second column indicates those re- 

 corded from the Chalk-rock of Cambridgeshire.) 





Dover. 



Chalk-rock 



of Cam- 

 bridgeshire. 



Ventriculites impressus, T. Smith 



mammillaris, T. Smith 



•55- 









Sponsre (species) 



Ooscinopora infundibuliformis, Goldf. 



t PhiUips, Trans. Oeol. Soc. ser. 1, vol. v, p. 24. 

 I Whitaker, Mem. London Basin, p. 32. 



§ Barrois, Ann, Soc. G-eol. du Nord, vol. v. p. 400 ; Barrois, Bull. Soc. Geol. 

 Fr. series 3, t. 2, p. 416. 



