OF THE UPPER CRETACEOUS TN WEST SUFFOLK AND NORFOLK. 585 



t 



bridge and Hertfordshire *. It consists almost entirely of fine 

 amorphous material, with but few recognizable shell-fragments and 

 Foraminifera ; but north of Shouldham these become much more 

 abundant, and the chalk assumes a firmer texture. 



The hard white chalk previously referred to as underlying the 

 Belemnite-marls closely resembles the white chalk with clean 

 fracture noted by us f as occurring at varying distances below the 

 Belemnite-marls of Hertfordshire and Cambridge. The single cells 

 of Foraminifera increase in quantity, and it would appear that 

 the change in the lithological character of the Chalk may be due to 

 some extent to their presence. This bed was noted as far as 

 Hillington, where it forms a marked feature in the pit-face ; beyond 

 this to the north it was lost. 



Grains of glauconite, which are to be found in almost every 

 specimen of the Chalk-marl, do not occur commonly in the Grey 

 Chalk (except at particular horizons in certain beds, as the " Rag" 

 of Bedfordshire) ; of nearly 150 specimens from this horizon alone, 

 from various localities, only one contains them. Minute grains of 

 quartz extend a little distance up into the Grey Chalk, where the 

 passage between it and the Totternhoe Stone is not abrupt ; the 

 same remark will also apply to the grains of glauconite. 



Mdhouvn Rock. — In thin sections this rock also presents the same 

 characters through Suffolk and Norfolk that have already been 

 described by us. Like that of Cambridge and Hertfordshire, it is 

 full of fragmentary pieces or nodules of chalk, not unlike that which 

 forms the top of the Grey Chalk beneath it, and these are imbedded 

 in a matrix which frequently contains a large proportion of coarse 

 shell-fragments. 



There is also at this horizon a remarkable increase in the quantity 

 of single Foraminifera! cells ; in some of the less nodular and shelly 

 specimens they are exceedingly abundant, and form a large part of 

 the material of the Chalk. 



Although these forms are often conspicuously abundant (see 

 ante), there is no other horizon below the Chalk Rock where, so far 

 as we know, they play so important a part in the formation of the 

 Chalk. They are generally referred to as the disunited or primordial 

 cells of Foraminifera ; but it is singular that with their increase 

 perfect forms do not become more abundant. 



§ 4. Chemical Composition of the Gault and Chalk-marl. 



By the kindness of Dr. W. Johnstone, F.G.S., and Mr. W. D. 

 Severn, we are able to furnish some information concerning the 

 chemical composition of the beds referable to the Gault and Chalk- 

 marl in West Norfolk. 



It has been stated (pp. 547, 549) that the marls which we refer 

 to the Upper Gault, near Roydon and Grimston,'are so calcareous as 

 to have been mistaken by some geologists for Chalk-marl. The 



* Quart. Journ. Geol. Soc. vol. xlii. p. 216. 



t Op. cit. 



