TRANSACTIONS OF SECTION C. 657 



WTiilst in Yorkshire the following zonal divisions are recognised by Professor 

 Prestwich :— 



Zone of Belemnitella mucronata . . . ~\ nu ^\ ■ u 



Marsupites (testudinarius) and sponges . / ^^^^^ without flints. 

 „ Micraster-cor-aiiguiiium .... Chalk with flints. 



' The typical white chalk,' says Professor Prestwich,' ' extends from England 

 through the North of France, South Belgium, East Holland, "Westphalia, 

 Hanover, Denmark, South Sweden, the coast of Pomerania, Poland, Silesia 

 Russia ; then in one direction to the Crimea, and in the other, with intervals, to 

 the south of the Ural Mountains. The pure earthy white chalk is not found out- 

 side these districts.' 



By way of comparison it will he necessary to select, as a type section of the 

 Upper Chalk in France, the petrological zones of M. A. d'Orbigny, which, 

 according to Professor Hebert, may be tabulated as follows : — 



Zone of Belemnitella imicronata . . Iileudon, Epernay. 



,, „ quadrata . . ., „ 



„ Micraster-cor-angnhium . . Chalk Cliffs east of Dieppe. 



„ „ cor-testudinarium . „ „ west of Dieppe. 



The most typical zonal succession of the Upper Chalk known to me is found 

 in the neighbourhciod of Salisbury, and from this district I have examined a mass 

 of well-preserved polyzoa, which had been collected by Dr. Blackmore and his 

 friends ; and it will be more convenient for me to work the other horizons by 

 reference to this : 



Feet. 



A. Zone of Belemnitella mucronata about 100 



B. „ ,, quadrata ....,,, lOO 



C. ,, Offirsvjntes testudinarius a,nd Ilolader 2nlula . „ 150 



D. ,, Micrastcr-cor-angiiinnm .....,, 100 



E. „ ,, ,, testudinarium .,,.,„ 50 



The Belemnitella quadrata zone is largely developed at Salisbury because it is 

 worked for the manufacture of whiting, and I think we may take the collection of 

 Dr. Blackmore, derived from this particular zone, as fairly representative of the 

 forms of the horizon. The other zones have yielded a fair proportion of the forms 

 submitted to me for examination, some of which are quite new to the British 

 Upper Chalk, or new altogether. From the neighbourhoods of Gravesend and 

 Chatham I have also a fine series of polyzoa, many examples of whicli are free 

 from the matrix, while others — and these are some of the best of the forms — are 

 attached to flints ; details, however, of the species could not be given in this brief 

 abstract of my contemplated work. 



It was while collecting information for a full description of the polyzoa of the 

 whole of the cretaceous rocks, that my attention was drawn to certain peculiarities 

 of the fossils under consideration, and which seemed to me to separate the 

 polyzoa of one bed from that of another ; but though the species from one bed 

 were not, on the whole, widely divergent in character, the fades of alhed forms 

 generally was well marked, or at least peculiar. These divergencies, therefore, I 

 do think merit something more than a mere passing notice. 



Of coujse, in giving specific or varietal details of our British cretaceous 

 polyzoa it will be necessary to work along lines so ably planned and utilised by 

 M. A. d'Orbigny in his palajontological studies, but any slavish adherence to his 

 plan of characterising, or even of classifying species, would retard rather than 

 advance our knowledge of the zonal distribution of the polyzoa. Let any one, 

 however, who is at all acquainted with the polyzoa of the cretaceous formation, 

 select and carefully study the species belonging to various genera characterised by 

 the specific name Meudonensis d'Orb. or Parisiensis d'Orb., and he will soon find when 

 correlating British forms bearing somewhat similar characters to the species 



' Geology, vol. ii. 1883, for Cretaceous zones generally, pp. 299-30P, 

 1891. "^"^ U U 



