Or THE UPPER CRETACEOUS IX WEST SUFFOLK AND NORFOLK. 587 



Just as this limestone lithologically resembles the harder beds of 

 the Chalk-marl, though it holds fossils which are characteristic of 

 the Gault, so also there is a resemblance between the Boydon 

 marls and the softer Chalk-marls of the south of England, as will 

 be seen by comparing the analysis above given with the following 

 (A being one by Prof. Voelcker, of a Wiltshire Chalk-marl*, B one 

 by Prof, Way, of a soft marl, near Farnham, in Surrey f , and C by Mr. 

 J. W. Knight, of the Chalk-marl at Horningsea near Cambridge) : — 



A. B. C. 



Insoluble residue (silica, &c.) 22-80 21-35 16-60 



Soluble silica 2'16 .... 



Carbonate of lime 70-80 70-88 69-00 



Carbonate of magnesia .... 1*72 -75 1-80 



Sulphate of lime 2-65 -35 .... 



Potash and soda traces 1-90 2*30 



Alumina and iron 1-02 2-31 3-70 



Organic matter and loss .... 1-00 .... 6*60 



99-99 99-70 100-00 



The proportion of carbonate of lime is a little larger than in 

 the Boydon marl, but near enough for us to conclude that the latter 

 was formed under such conditions of depth and distance from land 

 as afterwards prevailed in the south of England during the formation 

 of the Chalk-marl ; consequently we may infer that the Gault sea 

 in Norfolk was deeper and more distant from land than the Gault 

 sea of the south and centre of England. 



If we now compare the analyses of Chalk-marl, or even that of 

 the harder and more calcareous bed at Earnham, with analyses 

 of the beds at the base of the Chalk at Hunstanton, we shall see 

 how much more calcareous the representative of the Chalk-marl 

 becomes in Norfolk. The following analyses of (A) the " Sponge- 

 bed " and (B) the Inoceramus-hed have been kindly placed at our 

 disposal by Dr. W. Johnstone : — ■ 



A. B. 



Insoluble silica 3-17 3'38 



Lime 53-23 51-50 



Carbonic acid 42-29 40-54 



Phosphoric acid *29 *16 



Sulphuric acid traces *09 



Alumina *35 *35 



Peroxide of iron . *32 *50 



Manganese traces *47 



Magnesia *75 '25 



Sodium chloride traces *75 



Moisture and org. matter . . traces 1*40 



100-40 99-39 



* Journ. Bath and W. of Engl. Soc. ser. 2, vol. vii. p. 240. 



t Journ. Boy. Agric. Soc. vol. xii. p. 551. In this, after combining the mag» 

 nesia, the sum of C0 2 CaO has been taken as giving the amount of CaCO , 

 though the amounts are not in strict theoretical proportion. 



