NEAR STIFFORD, ESSEX.
185
in proportion to the distance from the nearest shaft-like opening
(a Fig. 2), in another it increased for a few feet and then diminished
for a space (b Fig. 2). Of course a subsidence, not improbably
taking a shaft-like form, would be likely to occur, sooner or later,
wherever the chalk roof was unusually thin, as well as at the site of
the former shaft. And, considering the closeness of the shaft-like
openings to each other, it seems probable that one was where the
shaft formerly existed, and the other where the chalk roof had been
left dangerously thin. The original shaft was most likely from three
to four feet in diameter, and on the disuse and stopping up of the
pit, was probably closed by means of faggots, on which earth was
thrown and trodden down till it formed a hard, compact mass. This
might remain as an efficient stopper for centuries in spite of the
decay and disappearance of the woody material beneath, though
liable to sudden downfall from the effect of an unusually heavy and
long-continued rain, or some other special influence.
There were many pick marks of ordinary size and appearance in the
Chalk of the irregularly situated chambers below. The rubbish cover-
ing the bottom of the pit may possibly have prevented us from seeing the
full extent of the workings, but, judging from what we saw, they may
have extended to a distance, here and there, of twenty or twenty-five
feet from the centre of the shaft, supposing it to have been in the
centre of one of our two openings. The purpose of the excavators
seems to have been simply the extraction of Chalk for agricultural
purposes. The Chalk in the district (coloured blue in the geological
map accompanying our Denehole Exploration Report, Essex
Naturalist, vol. ii, plate v.) though uncovered hereabouts by
any deposit the limits of which could be mapped, and frequently
only a few inches below the surface, is often, as in the case
before us, at such a depth as to make a Chalk-well a more con-
venient mode of getting it—where but a moderate quantity is
required for farming purposes—than a small open Chalk-pit.
A large open Chalk-pit, which has been disused about thirty years,
and is now much overgrown by trees and other vegetation, may be
seen between the site of these subsidences and "Chalk Pit Farm,"
while other disused open pits appear in various directions in the
immediate neighbourhood. In two spots close to the southern
boundary of the large Chalk-pit just mentioned are to be seen old
1 "Chalk Pit Farm" of the six-inch Ordnance Map is "Sugar-loaf House" on the old one-
inch Ordnance Map.