LENHAM BEDS. 
45 
The principal place where Pliocene fossils have been obtained 
is in a large Chalk pit half-a-mile north of Lenham. A sketch 
(Fig. 8) made in 1886 will explain better than words the mode 
of occurrence of the ironstone at this spot. In the distance 
clumps of fir occupy the crest of the escarpment at a height of 
about 630 feet. A few feet lower, and touching the 600-foot 
contour-line, is the edge of the pit, which has been cut out 
of the face of the escarpment, here not very steep. To the left 
the ground falls towards a small lateral valley, in which another 
chalk pit is situated. To the right the pit was much obscured by 
talus at the time of making this sketch, but it has since been again 
worked. 
The Down above the pit is occupied by extensive sheets of 
clay-with-flints, underneath which occur patches of sand, clay, 
and fossiliferous ironstone. Beneath this superficial covering the 
Chalk is undergoing a constant process of solution, especially near 
the escarpment, where the beds are somewhat fissured and the 
water-level lies a long way down. 
I'he result of this solution is to enlarge pre-existing fissures 
until they expand into more or less cylindrical pipes. Then as 
the Chalk disappears the overlying insoluble matter quietly 
subsides, often so regularly that the originRl succession of the beds 
can still be made out, though individual hard layers have been 
shattered and pulled apart. These ‘‘pipes'’ in the Chalk are 
well known to geologists, but as single pipes are seldom followed 
to any great depth it is perhaps scarcely realized to what a distance 
they may descend. Indeed the only limit to their denth seems 
to be at the plain of saturation, or at some impervious bed. 
Turning again to our Lenham pit we see here and there on the 
face of the Chalk vertical black cylinders of clay and sand. 
These cannot often be seen stretching from top to bottom of the 
pit, for a mass of loose material like this is far too dangerous to 
be left to support its own weight. They are therefore generally 
cleared away in the upper part before they are broken into below. 
However, by watching one of these pipes for several successive 
years, or by talking with the quarrymen, one learns that every 
one of them continues upwards till cut off by the soil or by the 
clay-with-flints, and continues downwards beneath the floor of 
the pit. 
In the foreground of the sketch are numerous black mounds. 
These are relics of pillars of chiy left by the quarrying away of 
the Chalk around the pipes, these pipes being disturbed as little 
as possible, for the material filling them is quite valueless. The 
mounds used to form a conspicuous feature in this pit, and were 
especially noticeable when the sketch was made. Since that time 
they have been systematically pulled to pieces to obtain the masses 
of fossiliferous ironstone examined by the Geological Survey. 
The contents of these pipes generally consist of an external 
shiny slickensided layer of black clay coating the wall of Chalk, 
and an internal confused mass of unworn flints, clay, and ferruginous 
or glauconitic sand, sometimes mixed with lumps of fossiliferous 
ironstone or ferruginous sandstone. 
