LOVi'Elt OH ALK—SEDIMENTATION 
31 1 
the non-deposition of any chalky Cenomanian sediments above the 
sandstones in the coastal region of Devon, for a subsequent subsi 
dence would be very likely to change the course of the currents, 
and the central track of the strong current which had swept over 
Somerset and Dorset might very well have been diverted into a 
more southerly course, while its velocity would doubtless be at the 
same time diminished. It might still, however, be strong enough 
to prevent deposition of any kind over the area between Sidmouth 
and Lyme until the very close of the Cenomanian age. It is prob¬ 
able also that the establishment of such conditions was assisted 
by the slope of the sea floor, this being doubtless toward the north 
and east, so that the water was deeper in those directions.* 
Passing over the wide area of Midland and eastern England, in 
which the zone of Ammonites varians is more or less argillaceous, 
we come to the northern region of purer sediment, which extends 
from Stoke Perry in Norfolk across the Wash and through Lin¬ 
colnshire into South Yorkshire. In this region there are no coarse 
sandy deposits, and there is consequently less difficulty in imagining 
the conditions under which the beds were formed. 
The reduction of thickness and the more calcareous nature of the 
chalk shows that this portion of the sea floor was quite out of the 
range of the currents which carried muddy sediment. At Speeton, 
however, we evidently reach the border of a tract which was invaded 
by such a mud-bearing current, and the resulting deposit was a 
true chalk-marl. Having regard to the great distance between 
Stoke Perry and Speeton, about 112 miles, it does not seem likely 
that the current carrying mud to the latter was a branch of 
that which carried mud to the former; it is more likely to have been 
a distinct current flowing from the north or the north-east. 
It should be mentioned, however, that the comparatively coarse 
and shelly character of the Inoceramus-Beds near the base of the 
Chalk in this part of England testifies to the existence of a current 
strong enough to carry away the finer particles of chalky sediment 
that would otherwise have accumulated, leaving only the larger 
shell-fragments and the mineral grains. It is clear, however, that 
this was a ground-current sweeping the floor of the sea, while the 
mud-bearing currents may have been surface-currents. Conse¬ 
quently the current which is indicated by the Inoceramus-Bed 
may have come from quite a different direction, and possibly from 
the south-west, though there is really no evidence to decide from 
which direction it came. 
The Totternhoe Stone is a repetition of the conditions indicated 
by the Inoceramus-Bed, only they extended over a larger area of 
the sea-floor. Mr. Hill considers that the structure of the Tottern- 
hoe Stone may be attributed to the action of a gentle but steady 
current in bearing away the fine material which form^ so large a 
part of the beds above and below it (see p. 32b). Current action is 
* Subsequent consideration of this problem has led me to think that there 
must have been some unequal crust-movements in Cenomanian time. 
