ON CRETACEOUS POLTZOA. 305 



A. Zone of Belemniiella mucronala, &c. Chalk without flints. 

 D. ,, Micnister cor-anguinum, &c. Chalk with flints. 



By way of contrast, it will be only necessary for me to quote two of 

 the many palaeontological divisions of the Continental Chalk on account 

 of the correlation of these with our own British sections. In north-western 

 France the zonal divisions are, to a large extent, based on the strati- 

 graphical divisions of d'Orbigny, and are as follows : 1, Danian ; and 

 2, Senonian : — 



1. Danian, 



Zone of Nautilus Danicus. 



2. Senonian. 



A. Zone of BelemniteUa mucronata (Chalk with flints), Meudon. 



B. „ ,, quadrata (Chalk with flints), Epernay. 



D. ,, Micraster cor-aiiguinum, Chalk clitf east of Dieppe. 



E. ,, „ cor-testvdinarium, Chalk clifl" west of Dieppe. 

 (P.) Here, again, the zone of Holaster planus forms the top bed of the 



Turonian series. 



In all probability the Upper Chalk found in the neighbourhood of 

 Chatham may be placed in the zones marked D and E in the above sec- 

 tional divisions. Chatham is superficially separated from the Margate 

 and Rarasgate ontci'op by the supervening London Clay, but the Upper 

 Chalk must have been continuous from the Essex outcrop to Gravesend, 

 Chatham, and the Isle of Thanet ; also from Sussex to Dieppe. 



It is impossible for me, of my own knowledge, to give any information 

 i"especting the geology of Chatham and its vicinity. When the Polyzoa, 

 which will be elaborately dealt with presently, were sent to me by Mr. 

 Gamble, I asked him particularly to give some account of the zones in 

 which the more characteristic forms were found. In reply to this request 

 I received sketches of the several pits in which the Polyzoan material was 

 most abundant. [Since this was written I have spent three days with 

 Mr. Gamble— purposely in the interest of this report — to see for myself 

 the evidences on which the following remarks are based. I have seen 

 the various sections ; collected material — especially the ' Flint-meal ' re- 

 ferred to further on ; and, moreover, I have carefully examined Mr. 

 Gamble's private collection of Polyzoa, containing duplicates of nearly 

 all the forms sent to me from time to time.] 



Some of the adherent species of Polyzoa, such as Siomatopora, Fro- 

 boscina, and Diastopora, were found encrusting many ibssils ; such as 

 Micraster cor-anguinum, Ecliinocorys, and other echinoderms; but the 

 most abundant of the forms described were found in the ' FJint-meal,' 

 which was derived from the hollows of flints. To the protective 

 agency of this meal we owe the preservation of the mote delicate branch- 

 ing Polyzoa, together with a varied assortment of the spicula of sponges, 

 Foraminifera, Entomostraca, and other minute organisms.' 



' ' Speaking: of the cavity and the so-called 'meal' found in the now celebrated 

 Horstead Flint, Dr. G. Jennings Hinde suggestively remarks : — ' The cavity appeared 

 to have been completely inclosed by the flint, which had thus hermetically sealed up 

 in its interior and preserved vinharmed from mechanical injury a small portion of 

 the mud of the Cretaceous ocean.* — Fossil I'yponge Spicules, kc, p. 4. Munich, 1880. 

 G. J. Hinde. 



1892. X 



