184
ON SOME RECENT SUBSIDENCES
southerly course along the road (see Fig. 1.), we found two openings
in the ground (S), nearly cylindrical in shape, between 7 and 8 ft. in
diameter and 9 to 10 ft. apart. The sides of these shaft-like open-
ings showed a section consisting of:—
Feet.
Clay, red, unstratified, about ...... 8
Sand, yellow ... ... ... ... 2 to 3
Gravel, stones small, large green-coated flints
here and there ............ 1 to 2
Chalk
The Chalk was thus between 11 and 12 ft. beneath the surface.
At the first glance, when seen from above, the two openings looked
Fig. 2. Section at the Stifford Subsidences. Scale, 1 inch = 8 feet.
as though their sides were equally vertical in each case, but on
descending a marked constriction towards the bottom of the gravel
and top of the Chalk was seen in one of them.
Though the fall of the clay, sand, gravel, and chalk into the
workings below had blocked them up to a considerable extent, it
was possible to creep through a chalk-roofed excavation connecting
the two openings, and to note the identity of the two sections of beds
above the Chalk. The Chalk had been worked in various directions
somewhat irregularly, and without any regard for permanent stability.
Thus, while in one chamber the thickness of the chalk roof increased