In this way cave-deposits, with their contained remains, may
be hermetically sealed up and preserved without injury for an
altogether indefinite period of time.
In all caves in limestone in which deposits containing bones are
found, we have then evidence of three principal sets of changes.
(1.) A period during which the cave was slowly hollowed out by
the percolation of acidulated water; (2.) A period in which the
cave became the channel of an engulfed river, or otherwise came
to form part of the general drainage-system of the district; (3.)
A period in which the cave was inhabited by various animals.
As a typical example of a cave with fossiliferous Post-Pliocene
deposits, we may take Kent's Cavern, near Torquay, in which a
systematic and careful examination has revealed the following
sequence of accumulations in descending order:--
(a) Large blocks of limestone, which lie on the floor of the
cave, having fallen from the roof, and which are sometimes cemented
together by stalagmite.
(b) A layer of black mould, from three to twelve inches thick,
with human bones, fragments of pottery, stone and bronze implements,
and the bones of animals now living in Britain. This, therefore,
is a _recent_ deposit.
(c) A layer of stalagmite, from sixteen to twenty inches thick,
but sometimes as much as five feet, containing the bones of Man,
together with those of extinct Post-Pliocene Mammals.
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