310 THE ESSEX NATURALIST
Figure 2. Area of Subsidences. (Scale: 1" = 1 mile)
Mr. Holmes suggested, when the usefulness of the working
of these pits had finished (or possibly, I think, for safety reasons)
the shafts were 'probably closed by means of faggots, on which
the 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'.