THE CRETACEOUS ROCKS OF BRITAIN. 
344 
CHAPTER XXV. 
PHYSICAL AND GEOGRAPHICAL CONDITIONS IN THE 
TIME OF THE LOWER CHALK. 
1. Evidence of Current Action at the Base 
of the Chalk. 
The stratigraphical facts which have been recorded in connec¬ 
tion with the basement beds of this stage at different localities 
prove that some considerable physical changes took place at the 
time when these basement beds were formed. It will be worth 
while recapitulating some of these facts in order that the evi¬ 
dence of increased current-action may come more clearly before 
the reader. 
First, then, we saw that in Kent there was everywhere evidence 
of erosion at the top of the Gault; at Folkestone the sand of the 
Stauronpma bed is piped into the underlying Gault; near Burham 
the top of the Gault is cut off abruptly and overlain by a layer of 
pliospliatic nodules which have presumably been derived from it. 
At Eastbourne, in Sussex, there is an abrupt change like that at 
Folkestone, with a similar piping of Chloritic Marl into the under¬ 
lying stratum. In the Isle of Wight there is a variable set of beds 
at the junction of the two formations, but most sections show an 
horizon where the material of one bed is piped into another ; there 
are also layers of phosphatic nodules and lumps of partly phos- 
pliatised stone. 
Throughout the greater part of Dorset the uppermost bed of the 
Greensand exhibits every sign of having been exposed to the action 
of a strong current for some length of time (see pp. 93 and 108). It 
is a hard calcareous rock, the surface of which is often phosphatised, 
and it forms a great contrast to the soft glauconitic chalk (with its 
basement layer of phosphatic nodules) which overlies it. In East 
Devon there are similar signs of erosion and evidence that currents 
were active throughout the whole epoch of the Lower Chalk, for 
at the most western localities the Chalk Marl is represented by a 
few feet of shelly and quartziferous limestone, above which is 
another plane of erosion, and a total absence of anything to cor¬ 
respond with the rest of the Lower Chalk. 
In South Wiltshire and Hampshire there is generally more or 
less of a passage from one formation to the other, so that in this 
area a certain amount of deposition took place while erosion was 
