A. J. Jnkes-Broivne — Two Stages in Tipper Chalk. 307 



Holaster planus be included in the Upper Chalk or Senonian there 

 will be seven zones without reckoning that of Ostrea lunata. 



In the following pages I shall endeavour to show that the Upper 

 Chalk or Senonian of England, France, and Germany really contains 

 two distinct faunas, and is consequently divisible into two stages 

 as distinct as the Cenomanian and Turonian. I shall also consider 

 the range of some of the component members of these faunas with 

 the special object of determining the most natural line of divis^ion 

 between these two stages. 



French geologists long ago recognized the difference between the 

 assemblages found in the lower and upper parts of d'Orbigny's 

 Senonian stage, but they liave never tabulated the fossils with the 

 view of demonstrating the precise amount of tliis difference. They 

 have divided the ancient ' Senonian' into two parts, and have given 

 these parts definite names, but regard them as sub-stages and not 

 as primary divisions of the series. German geologists have also 

 recognized a division into Unter- and Ober-Senon, but they do not 

 adopt the French names and they do not agree as to the horizon at 

 which the plane of separation should be drawn. 



To tabulate the whole Senonian fauna would be both a laborious 

 and unnecessary task. If it really comprises two different assemblages, 

 their diversity should be made apparent by a separate tabulation of 

 two or three classes of organisms and especially W the Cephalopoda. 

 This we shall find to be the case, but as Cephalopoda are not 

 everywhere abundant I shall supplement their evidence by that of the 

 Echinoids and the species of the genus Inoceramus. 



Further, in order that the tabulated lists may be readily compared 

 with one another the zones of the Senonian in England, France, 

 and Germany must be correlated with one another, and as the zonal 

 nomenclature has not yet been iinified and perhaps cannot ever be 

 made the same for all three countries, I have prepared a table of 

 equivalent zones for reference. 



The French and English zones are easily correlated because we 

 have practically adopted the French zones, but in Germany the case 

 is different. In the latter country the beds which contain typical 

 i\[icraster cortestudinarium are known as the ' Cuvieri-planer ' from 

 the abundance of Inoceramus Cuvieri, and are placed at the top of the 

 Turonian stage. This zone is overlain by a great thickness of grey 

 marl and marly clay in which there are few Echinoderms, but a large 

 number of Inocerami and Cephalopoda, the species indicating that these 

 beds represent our zone of Micranter coranguinum with perhaps some 

 of the underlying zone of M. cortestudinarium. These marls have 

 been called the ' Emschermergel ' from their development near Ems, 

 and Dr. Sehliiter regarded them as forming a separate stage between 

 the Turonian and Senonian, but others moie correctly consider the 

 special character of the fauna as due to special local conditions of 

 deposition. 



The 'Emscher' Beds are succeeded by a set of sandy marls which 

 Sehliiter classed as Unter-Senon and divided into three zones, with 

 the indices of (1) Marsupites omatus, (2) Pecten muricatiis, and 

 (3) ScapJiites hinodosus. The two higher zones correspond with that 



