OF THE UPPER CRETACEOUS IN "WEST SUFFOLK AND NORFOLK. 591 



tliat it contains a peculiar layer of reddish marl or clay, which 

 remains as a basement-bed after the more Gault-like material has 

 thinned out. 



3. That the Norfolk Gault, as a whole, is much more calcareous 

 than the Midland Gault, and that its upper portion cannot be called 

 a clay, but is a light-grey chalky marl, with occasional layers of 

 yellowish-grey limestone. 



4. That the fossils of these limestone bands decide the real age of 

 the beds. 



5. That microscopical examination shows a decreasing amount of 

 inorganic matter (quartz, mica, and felspar) as the beds are traced 

 northward, with an increasing proportion of organic material (Fora- 

 minifera and shell-fragments), which becomes very large in the 

 E-oydon and Grimston Marls. 



6. That there is an entire absence of anything comparable to the 

 malmstones, ragstones, or glauconitic sands of the so-called Upper 

 Greensand. 



The increasing amount of calcareous matter in the Gault as it is 

 traced northward through Norfolk is, we consider, a fact of much 

 importance. It is evident that in passing from Dorsetshire to 

 Norfolk we travel further and further away from the source of the 

 mechanical sediment, and get nearer to oceanic conditions. The 

 quartzose sands of the so-called Upper Greensand appear to die out 

 in North Wiltshire or in Berkshire, the malmstones die out in Buck- 

 inghamshire, and marly clays of the Upper Gault take their place 

 to the northward ; in Bedfordshire this Upper Gault is very cal- 

 careous, and it is still more so in Norfolk, where the Lower Gault 

 also becomes calcareous, and the whole formation gradually passes 

 into a thin calcareous deposit. 



Just as the upward succession of the Gault clays at Folkestone 

 from the dark-blue pyritous clay of the Lower Gault to the light- 

 grey marly clay of the Upper Gault, indicates in all probability a 

 deepening of the sea in which they were deposited, so the lateral 

 passage from the argillaceous Gault of Bedford and Cambridge to 

 the marly cla3 _ s of West Norfolk means an increasing depth of water 

 and distance from land in this direction. 



These considerations are, in our opinion, quite sufficient to explain 

 why the Upper Gault in the centre of West Norfolk bears so great 

 a resemblance to Chalk-marl, and why it contains layers of lime- 

 stone and red clay. 



This chalky marl is, in fact, the deep-water representative of the 

 Upper Gault and so much of the Upper Greensand as can be show^n 

 to be the equivalent of the Upper Gault. 



Chalk-marl. — With respect to the Chalk-marl itself, we may 

 summarize our results as follows : — 



1. That it maintains its average thickness as far as Stoke Ferry,, 

 but then thins rapidly northward, and decreases to 18 feet at 

 Hunstanton. 



2. That its lithological characters alter, the upper part becoming 

 harder and whiter before it begins to thin ; hard beds also make 



2e2 



