LAMPLUGH : GLACIAL SECTIONS. 
35 
The clay is chocolate-coloured, and very fine and tough. It is 
beautifully laminated, and in places ripple-marked, and contains 
no pebbles nor other foreign admixture, save in its lowest layers. 
It rests on an eroded surface of the ' Basement Clay,' which has 
been worn into deep hollows. Upwards, it is cut off abruptly by 
the Purple Clay wherever it rises much above beach level, ending 
thus a littlie beyond the limits of my section on both sides. 
About 350 yards beyond the southern termination of Fig. 2, 
just before the laminated clay is cut out as described, it passes 
upward into sand with clay partings, which are in one place seven 
feet thick. This is only seen for a short distance ; the base of 
the purple clay above is forced down irregularly over it, and 
shows slickensides. A similar sand-bed remains above the lamin- 
ated clay for a short distance, on the other side of the town, and 
I have no doubt that sand has once been continuous at this 
horizon, and has nearly all been swept off during the deposition of 
the Purple Clay. 
The laminated clay completely fills the deep and wide hollow 
in the Basement Clay on the beach, near the northern end of 
Fig. 1, so that it has here a thickness of about 16 feet: else- 
where it rarely exceeds four or five feet. The foundations of the 
sea-wall were placed in this hollow, with the recorded results. 
There is a thin seam of chalky gravel between the laminated 
clay and the underlying boulder clay in the bottom of the hollow, 
and this, whenever tapped, yields copious supplies of very pure 
water, which wells out at high tide but ceases to flow at ebb. A 
row of piles driven down into the Basement Clay in front of the 
wall (with the hope of staying its further advance) forms in this 
way a line of fine ebbing and flowing springs ; and an iron tube, 
which has been let down behind the wall, discharges a strong and 
continuous jet at high tide. The well-known ebbing and flowing 
spring in the harbour is probably supplied from the same 
source. 
