A. J. Jukes- Brotciie — Two Stages in Upper Chalk. 305 



nomenclature of the Chalk will liave to be abandoned, for tlie 

 formation will then be divided into four parts instead of three, so 

 that the names Lower, Middle, and Upper could no longer be retained. 

 The time has hardly yet arrived for this change to be made, but 

 Mr. Hill and I wish to express our belief that it will come, and that 

 some scheme of nomenclature more resembling that of the French 

 geologists will have to be adopted for the Upper Cretaceous Series of 

 England". 



JSTearly ten years have passed since the above was written, and the 

 furtlier researches which have been niade since that time iiave only 

 tended to strengthen our belief, but have at the same time shown the 

 wisdom of waiting for more evidence before deciding where the line 

 between the two divisions of the Upper Chalk should be drawn. 



A more careful consideration of the (juestion has convinced me that 

 the distinction between these two portions of the Upper Chalk is less 

 marked in England than it is in France or Germany. In England 

 there is little variation in the lithological character of the deposit, 

 which consists of nearly pure chalk throughout a thickness of some 

 1,100 feet. As a consequence the fauna has a similar facies through- 

 out, and there is a complete passage from each zone to the next one, 

 so that many species range from one into another. Moreover, all 

 kinds of Cephalopoda except Belemnites are rare, so that it is 

 impossible to use Ammonoids as zonal indices, and we are obliged to 

 have recourse to Belemnites and Echinoderms. 



On the other hand, in parts of France and Germany the pure chalk 

 passes into other kinds of calcareous deposits, such as argillaceous 

 marl, marly limestone, Bryozoan and siliceous limestones. Moreover, 

 Ammonites are much less rare, and M. de Grossouvre has shown that 

 a reliable zonal classification can be established on the recorded 

 occurrences of the different species. There is also a greater number 

 and greater variety of Echinoderms on the Continent than in England, 

 so that the faunal difference between the one set of zones and the 

 other is more apparent. Probably when the Brachiopoda have been 

 more fully studied they also will show a more restricted range of 

 species and varieties. 



The cause of this more marked difference of fauna on the Continent 

 is doubtless the fact that parts of the European region were land 

 during most of the Cretaceous period, and that there was a greater 

 variety of life in the shallower waters near the land-tracts than in the 

 deeper water which lay over the British area and the greater part of 

 the Paris Basin. 



Before proceeding any farther it is necessary to make some remarks 

 on the zonal division of the Upper Chalk. Until recently only six 

 zones were recognized as its components in the South of England, but 

 so long ago as 1899 and 1900 Mr. A. W. Bowe remarked that the 

 true Actmocamax quadratus is so rare a fossil in England that Ojfaster 

 'pilula would be a better index fossil for the zone which has hitherto 

 gone by the name of the former. At the same time he pointed out 

 that A. quadratus only occurs in the higher part of the zone, the 

 form found in the lower part being A. granulatus. 



More recently Messrs. Griffith & Brydone have proposed to divide 



DECADE V. — VOL. IX. — NO. VII. 20 



