The sketch of Bethnal Green (Fig. 80) was made just as the churchyard
was about to undergo a healthy conversion, and it marks a very long
period of inaction.

The Plumstead case (Fig. 81), though less extreme, is even more
informing, as it seems to measure the rate at which the disappearance
goes on; the dates on the three stones coinciding accurately with
their comparative depths in the ground. Whether the motion of the
earth has any influence in this connection need not now be discussed,
because the burying of the gravestones may be accounted for in a
simple and feasible manner, without recourse to scientific argument.
It is undoubtedly the burrowing of the worms, coupled with the wasting
action of rain and frost, which causes the phenomenon. Instead,
however, of the sexton's supposititious century, the period required
for total disappearance may more accurately be regarded as from 200
to 250 years. It has been found by careful observation in a few random
cases that the stones subside at the rate of about one foot in forty
or fifty years, and, as their ordinary height is from 5 feet to 5 feet
6 inches, we can readily tell, providing the rate rules evenly,
the date when any particular stone may be expected to vanish. In
confirmation of this theory is the fact that scarcely any headstones
are discoverable of a date earlier than 1650, and whenever they have
been left to their fate the veterans of 150 years have scarcely more
than their heads above ground. Wherever we find otherwise, it may be
assumed that conscientious church officers or pious parishioners have
bethought them of the burial-ground, lifted up the old stones and set
them once more on their feet. Of recent years there has grown up and
been fostered a better feeling for the ancient churchyards, and the
ivy-clad churches of Hornsey and Hendon may be cited as examples