144 ON SOME SECTIONS BETWEEN W. THURROCK AND STIFFORD,
saw the embankment of the new railway leaving that of the London
and Tilbury close to Mill Lane, and sweeping round in a north-
westerly direction so as to cross the Grays and West Thurrock road
a little westward of Home Farm. A few yards south of the point
marked a on the map, the embankment is gradually replaced by a
cutting, which is 18 to 20 ft. deep at a, will ultimately be 30 ft. or
more at b, and ends a few yards north of c, where it is about 20ft.
in depth. The railway, as shown on the map, will be found to be
laid down with a sufficient approach to correctness for geological
purposes, though it has, of course, no pretensions to perfect
accuracy.
The first good section is at a, where the railway cuts through
the corners of two fields, and at the same time crosses the 50 ft.
contour line. There the junction of the Chalk with the sand and
gravel of the Thames Valley may be clearly seen.
Perhaps the most interesting object visible at this point was a
large pipe in the Chalk filled with sand and gravel. The course of this
pipe having been less vertical than usual, it presented the appearance
of a mass of sand and gravel entirely surrounded by solid Chalk.
Sections of pipes of this kind being comparatively uncommon, and
presenting at first sight an apparently abnormal aspect, the existence
of this one at a, on the eastern side of the cutting, seems worth
noting.
The height of the surface of the ground above Ord. datum
(marked by figures on the map), which is 50 ft. at a, becomes 90 ft.
or thereabouts at b, and sinks at c to between 70 and 80 ft. Though
the greater part of the cutting between a and c had not been
excavated to its full depth at the date of our visit, enough of the
surface material had been removed to show that only a sprinkling of
pebbles with about a foot of soil overlie the Chalk between those
points. About b, the workmen, while removing the uppermost
seven or eight feet, came upon some old workings in the Chalk,