CRETACEOUS SEEIES IN LINCOLNSHIEE AND TORKSHIEE. 357 



finer material at this horizon, leaving the coarser shell-fragments, 

 thus probably retarding deposition and affording conditions favourable 

 to the growth of the fauna which always occurs so abundantly at 

 this horizon. 



Besides the shell- fragments which form the major part of the 

 material of the Grey Bed, there are many Foraminifera and an abun- 

 dance of glauconite-grains, so that in its composition it will compare 

 with the Totternhoe Stone. 



Tlie Grey Chalh. — Little need be said concerning this division. 

 Lilve that below, the " Grey Bed," it consists in great part of fine 

 amorphous material of a purely calcareous nature in which shelly 

 fragments and Eoraminifera occur in varying proportions. 



The Belemnite-Marls. — The material of which these marls consist 

 is probably derived from the erosion of the chalk below ; but inor- 

 ganic matter, in the form of fine amorphous material and measurable 

 particles (? of quartz), again makes its appearance, although the 

 proportion to the whole does not seem large. Microscopic examina- 

 tion affords no clue to the reason of the dark colour of the marls in 

 North Lincolnshire and Yorkshire. 



Middle Cliallc. — Specimens which I have examined from the 

 base of the Middle Chalk show the same marbled or nodular structure 

 which characterizes the Melbourn Eock, and also the remarkable 

 increase in the amount of single Foraminiferal cells, which though 

 quite as abundant for a space at other horizons, notably in the 

 Hunstanton Limestone of Lincolnshire and Yorkshire, do not per- 

 sistently and regularly form so large a proportion of the material 

 of the Chalk as they do here. 



Chemical Composition of the Chalk in Lincolnshire 

 and YorJcshire. 



Mr. J. W. Xnights of Cambridge has made for me general analyses 

 of several specimens of the Chalk of Lincolnshire and Yorkshire ; the 

 results are as follows : — 



An analysis of the Bed Chalk of Lincolnshire is given in the 

 " Geology of East Lincolnshire " *. The comparison of this with the 

 analysis by Dr. Johnson f of the Hunstanton Limestome shows that 

 the Red Chalk of Lincolnshire contains a higher percentage of 

 calcareous matter than that of Hunstanton. But different con- 

 ditions of deposition are manifest on the comparison of these 

 two with two of the upper and lower parts of the Hunstanton 

 Limestone at Speeton. For convenience of reference I give below 

 a general tabular view of the proportions of the principal elements 

 of the Gault and its equivalent, the Hunstanton Limestone, from 

 various localities. 



It will be seen on referring to this that the amount of insoluble 

 siliceous matter has risen from 7' 50 per cent, at Hunstanton to 42*40 

 per cent, in the lower, and 24*60 per cent, in the highest part of 



* Mem. Geol. Surrey, p. 33. 



t Quart. Journ. Geol. Soc. vol. xHii. p. 588. 



