﻿362 A. J. Juices Browne — On the Upper Greensancl, etc. 



either indigenous or derivative ; it has on this account been generally 

 confused with the sands below, and the two together have been 

 called Chloritic Marl. Dr. Barrois, however, has shown that it is 

 divisible from these sands in Hampshire, and it seems probable that 

 the latter are lenticular beds belonging to the P. asper zone some- 

 times attaining a thickness of 10 or 15 feet and sometimes thinning 

 out altogether, while the thin bed of sandy marl with glaucouitio 

 and phosphate nodules has a wider estent, and is probably to be 

 found at the base of the Chalk-marl all round the Weald ; its exist- 

 ence is very marked in the neighbourhood of Maidstone, where it 

 directly overlies the Gault, as at Cambridge, without the interposition 

 of any Upper Greensand strata whatever. 



The thickness of this bed is rarely more than 3 or 4 feet, but 

 it passes gradually upwards into the Chalk-marl from which it is 

 inseparable, except so far as its green grains and phosphate nodules 

 give it a character of its own. Thus it is clear that the narrow zone 

 of glauconitic marl lying at the base of the Chalk cannot be con- 

 sidered as forming a separate division, and therefore does not merit 

 such a name as that of Chloritic Marl, which at once suggests a 

 comparison with the Chalk-marl, and gives it an importance far 

 greater than it possesses ; moreover, it has often been pointed out 

 that the name itself is based on a misconception, in as much as the 

 green grains are not composed of Chlorite but Glauconite, and I 

 therefore agree with Mr. Whitaker and Mr. Price in advocating the 

 entire abandonment of the name. 



Since, however, the bed itself does exist as a zone subordinate to 

 the Chalk Marl, it is desirable that some name indicative of this 

 should be assigned to it ; Mr. Davidson and Mr. De Eance have 

 called it the zone of Scaphites csqualis, and perhaps that name can be 

 adopted ; at the same time it may be observed that this fossil is both 

 of wide and partial distribution ; it is known to occur both in the 

 beds above and below, while in some areas, as at Cambridge, it 

 does not seem to exist in the zone of which it is supposed to be 

 characteristic. It may therefore be found more convenient to indi- 

 cate this horizon by one of the numerous sponges, which it every- 

 where contains, and which are now being described by my friend 

 Mr. W. J. Sollas. Or, lastly, it may have to be amalgamated with 

 the horizon immediately succeeding it, which Dr. Barrois calls the 

 zone of PlocoscypJda mceandroides, further information being required 

 concerning the persistence of this band and its relation to the marl 

 below. 



Finally, it is desirable that some more clear definition of the 

 Upper Greensand should be given. I remember Prof. Eamsay once 

 observing that Gault and Greensand were the same thing, and 

 doubtless they are in the sense that no hard and fast stratigraphical 

 line can be drawn' between them, but taken as a whole it is founti 

 that the series can be divided into three groups of beds, each con- 

 taining a peculiar fauna of its own, and worthy of a separate name. 



Dr. Barrois says that the English Upper Greensand consists of two 

 parts, which he calls the zones of Am. iiiflatus and Pecten asper, but 



