200 NATURAL SCIENCE [September 



Chalk (including the zone of Stauronema). Here also the true rela- 

 tions of the fauna are quite clear. 



In this study of the fauna of the English zone of Am. rostratus 

 I have excluded Echinoderms, because their evidence is not of first- 

 rate value ; in support of this opinion, I may quote that of Dr J. W. 

 Gregory of the British Museum, who has remarked that, "Echinids are 

 rather a clue to the conditions of formation of deposits than evidence 

 of their exact contemporaneity in age." Thus it may be quite true, 

 as Mr Lambert declares, that the affinities of the Echinoidea found 

 in the Gaize of Havre are Cenomanian, but their evidence cannot weigh 

 against that of the Cephalopoda which are most clearly not Cenomanian. 



Mr Dollfus quite omits to notice that I have appealed to the 

 Cephalopoda as affording the best criterion of the affinities of the 

 fauna of these beds. Let us see what this criterion proves. 



Erom the Upper Gault of Folkestone Messrs Price and De Eance 

 have recorded 3 1 species of Cephalopoda, and of these 1 2 range down 

 into the Lower Gault, and only 4 range into beds above. Similarly 

 in the Gaize of Devizes there are 20 Cephalopods, of which number 

 7 occur in Lower Gault and 4 range into higher beds. Both at Folke- 

 stone and Devizes Ammonites rostratus and A. varicosus are restricted 

 to the Gaize and Upper Gault, but in the counties of Buckingham 

 and Bedford, I have myself found both species in the Lower Gault. 

 In two cases they were in company with A. lautus and A. splcndens 

 about 30 feet from the base of the Gault which is there 200 feet 

 thick ; in a third case they occurred with A. intcrruptus quite near 

 the base of the Gault. With respect to the upward range of A. rostratus, 

 it passes upward into the green glauconite sands above the Gaize, 

 both in Wiltshire and Dorset, and where the Chert Beds are absent, 

 I have found it within six or seven feet (two metres) of the top of 

 the Upper Greensand. No Ammonites have yet been found in the 

 Chert Beds, but A. rostratus has never been found above them. 



Next let us consider the true Cenomanian group of Cephalo- 

 poda : — Ammonites varians, falcatus, mantclli, navicularis, rotoma- 

 gensis, Scaphites acqualis, Turrilitcs costatus, tuhereulatus. No one 

 who has collected along the south coast of England or at Wissant, 

 or at Havre, could doubt where these species first set in as common 

 fossils ; they come in with Stauronema carteri and A. laticlavius in 

 what is generally called the Chloritic Marl. 



It is only occasionally and locally that any of them occur below 

 this horizon, but so far as my experience goes not one of them 

 ranges further than six feet below it. A. varians, falcatus and 

 navicularis are not uncommon at the top of the Greensand between 

 Warminster and Maiden Bradley, but are not associated with A. 

 rostratus ; the bed in which they occur is evidently a passage bed 

 from Greensand to Chloritic Marl. 



