CONTRIBUTIONS TO PLEISTOCENE GEOLOGY. 57
MILWOOD LANE PATCH.
The most important patch of gravel extends from near the
Upminster and Grays Railway on the west to Clockhouse Lane
on the east, having a length of about three-quarters of a mile,
and a breadth of a little under half a mile. Milwood Lane crosses
the patch from north to south, dividing it into two equal por-
tions. The altitude which the surface of this patch attains is
between 90 and 116 feet O.D.
Account of Sections.
a. At the junction of the footpath on the east side of Milwood Lane with
the lane south of the Stifford Board School there is a small ballast pit which
shows about four feet of fine gravel and sand. In this we found a worn fragment
of Triassic sandstone.
b. A little further south there is exposed in the road-side by Milwood House
two or three feel of gravel and sand ; below this, going down the slope, is seen
sand and then a little chalk rubble ; lastly, and still lower, several feet of brown
sand, with gravel here and there, occur. This last is a mixture of Thanet Sand
and Drift, and is due to the piping action; but when seen for the first time, both
here and at other places in the district, it is apt to puzzle the observer.
c. Just to the south of this two fine sections are exposed on either side of the
lane. That on the western side is yielded by the upper working of the quarry of
the Thames Portland Cement Works (Gibbs' Pit), and the details of this are of
great interest. The northern face of the quarry is large, and shows about six
feet of gravel resting regularly on upwards of 40 feet of Thanet Sand. The
eastern face shows a wall of Thanet Sand about 30 feet in height, sunk into the
surface of which, near its southern end, are two large basins filled with gravel,
quite evenly bedded; the larger of these is about ten feet in depth and twice as
wide. The stratification of the gravel follows the curvature of the basins, thus
proving that these isolated patches owe their position to the "pipe" making
agent.
The great thickness of Thanet Sand preserved here at such a low altitude is
of interest, and its cause, as shown in the section, adds fresh evidence as to the
comparatively vast results which may be produced by the solvent action of
acidic water in limestone districts. The upper working is cut down to the
surface of the chalk, and no further in this quarry, and this surface is seen to have
been eroded by subterranean acidic water into a huge shallow basin or trough,
into which the overlying Thanet Sand and Drift have gently subsided. A point
worthy of note is afforded in the fact that, notwithstanding the dissolution of the
chalk, the Bull's Head bed of unworn flints between it and the Thanet Sand
receives no sensible augmentation to its development. This arises from the
comparative scarcity of beds of flint in the chalk of the district.
Close to the entrance to the pit from Milwood Lane a large rounded boss of
chalk protrudes into the overlying Thanet Sand. It is riven throughout its
entire mass into cubic or prismatic blocks, each of which has its sharp angles and
edges completely rounded off. The larger fragments are at the centre of the base
of this mass, and from this they radiate off, the fragments becoming smaller and
smaller as they near its periphery. The larger of the fragments are a foot in
length, and from this size every gradation may be traced into others which are