LOWER CHALK—NORFOLK. 
209 
iug to a creamy yellow tint. Of this limestone 3 or 4 feet are seen, 
resting directly on and passing down into the pale grey marls of 
the Upper Gault without anything like the usual glauconitic 
basement bed. In minute structure it is a purer and more com¬ 
pact form of the rock which overlies the basement bed at Should - 
ham. The only fossils seen were small Belemnites and a small 
species of Rhynchonella. 
A small pit about half a mile N.N.E. of Hoy don Church discloses 
fin important section, because it shows the whole of this hard whitish 
rock and some of the overlying chalk, the beds seen being as follow : 
ft. 
Hard greyish gritty chalk, weathering into flaggy pieces, and 
containing at the base a number of green-coated nodules - 6 
Very hard creamy-white chalk, piped at the top with material 
from above - - - -- 5^ 
It lias been ascertained by boring that this lower bed rests directly 
on the marly clay of the Gault (see Vol. i., p. 300). The importance 
of this exposure is that the gritty chalk is undoubtedly correlative 
with the “ Inoceramus Bed ” of Hunstanton. We think also that 
it is likewise the condensed equivalent of the central part of the 
Chalk Marl at Stoke Ferry, i.e., the greyish shelly chalk traversed 
in the boring mentioned on p. 208, just as the whitish chalky 
limestone below is the condensed equivalent of the softer Chalk 
Marl proved in the lower part of the Stoke Ferry boring. 
The great condensation which has taken place in the Chalk Marl 
as a whole, by the elimination of the marly or rather the argilla¬ 
ceous ingredient, is shown by the section obtained in the large 
chalk-pit at Dersingham. Here below the Totternhoe Stone about 
8 feet of hard creamy-white chalk is exposed, becoming rather 
greyer below; while a boring made through the floor of the pit 
in 1886 disclosed the following beds * : — 
. h. 
Hard greyish chalk, becoming greyer and more gritty below, 
with yellowish green-coated nodules near the base - - 8 
Very hard compact white chalk - - - - - - li¬ 
fe. Gault marls below. 
Here therefore the total thickness of the chalk between the Gault 
and the Totternhoe Stone is only 17-J feet, as compared with 75 
feet at Stoke Ferry. 
At Hunstanton it is only a foot thicker, and the section is practi¬ 
cally the same. See Fig. 50, which is reproduced from the paper 
by Mr. W. Hill and the author, already referred to. 
The hard white chalk which overlies the “ Bed Chalk ” of Hun¬ 
stanton has long been known as “ the sponge bed,” on account of 
the curious cylindrical bodies which it contains, and which resemble 
the stems of Siphonia , but do not exhibit any sponge structure. 
The succeeding grey shelly chalk is generally called the “Inocera- 
mu$ bed/'from the number of broken Inocerami which it contains. 
1 1 11 ■ '» ' ■ ■ .i . - - . “ ' . . .... ... ■ ■ Vi r 
* See Quart. Journ. Geol. Soc., Vol. xliii., p. 560 (1887). 
