﻿A. J. Jukes Broume — On the Upper Greensand, etc. 359 



Dr. Barkois' Classification. 



Having now reviewed the various descrijDtions and definitions 

 which have been given of the Upper Greensand and Chloritic 

 Marl up to the year 1875, I proceed to notice those given in the 

 recently published researches of Dr. Ch. Barrois,^ which have, I 

 conceive, gone far towards harmonizing the conflicting opinions 

 previously existing with regard to the constitution and im- 

 portance of these beds, and towards establishing a more natural 

 method of grouping the strata in this portion of the Cretaceous 

 series. 



In this work Dr. Barrels has shown that a proper understanding 

 of the Cretaceous system (as of all other systems) can only be 

 attained by one who unites the qualifications of a palaeontologist 

 with those of a field-geologist ; and no one, I think, can study the 

 pages of his " Eecherches " without admitting that he himself pos- 

 sesses these qualifications in an eminent degree. 



He has also reminded us, or rather takes for granted that we 

 remember what some of us seem apt to forget, that lithological 

 characters alone form untrustworthy foundation for rock-groups, 

 that the same stage or formation can be a clay in one distinct and 

 a marl or sandstone in another, that Gault may include sand as 

 well as clay, and that this is particularly the case with the Upper 

 Gault or zone of Ammonites injiatus. 



Working on these data he has determined the existence of a succes- 

 sion of pal^ontological zones from the Gault upwards throughout the 

 Chalk, and carefully followed them over the Cretaceous areas of the 

 British Isles. 



The first four of these zones are as follows : — 



1. Zone oi Amm. injiatus = Blackdown Beds. 



2. „ fecten asper ^^WsLvminster Beds. 



3. Chloritic Marl. 



4. Zone of Solaster subglobostis = Chalk Marl. 



Eegarding the first two of these divisions, he says (p. 71), "The 

 Upper Greensand, as defined by Berger, Ingiefield, Webster, Fitton, 

 and Ibbetson, appears to me everywhere divisible into two zones ; 

 the zone of Am. injiatus, and the zone of P. asper. The fauna of 

 the Upper Greensand, being a mixture of these two faunas, had of 

 necessity relations with both." Again at p. 105, " I had thought 

 that the lithological characters of the Upper Greensand would make 

 it a special division, distinct from the other horizons ; but I was 

 deceived, and in the Upper Greensand of the Isle of Wight, as in 

 that of the rest of England, there are two perfectly distinct faunas, 

 that of Blackdown and that of Warminster." The case, however, is 

 not quite so simple as would appear from this, for the lower and 

 clayey portions of the Amm. injiatus zone have always been ex- 

 cluded from the Upper Greensand ; the two zones therefore do 

 not exactly form its equivalent, since they include more than the 

 Upper Greensand. 



1 Eecherches sur le Terrain Cre'tace' superieur de I'Angleterre et de F Ireland, par 

 Ch. Barrels, D.Sc. Lille, 1876. 



