In this limestone cliff we shall find other borers, for you may see
even at a considerable distance how holed and honeycombed its surface
is; the cavities being so numerous, so close, and so irregular in
their direction, that the whole face of the rock is fashioned into
small sharp-edged shapeless points. Nor need we be long in finding
the industrious masons who thus rough-point acres upon acres, nay
miles upon miles, of limestone rock. Here in ten thousand orifices you
discern little double-tipped knobs of crimson flesh, which, as soon as
you disturb them, shoot at you a column of water and then disappear
within their fortress, having exhausted their artillery. The fishermen
know them well, and use them for bait, applying to them the familiar
but expressive soubriquet of Red-noses.[31]
It is not so easy to get at these as at the Pholades, because of the
superior hardness of the stone which they excavate. With the chisel,
however, we need not fail of uncovering a few, especially as their
burrows are but shallow. Here they are, half-a-dozen in a block as
big as your fist. Ugly, uncouth, bemired, the valves not nearly
containing the shapeless flesh, they are not particularly attractive
creatures, maugre the brilliant hue of their blushing siphons. Like
Mrs. Merrifield’s Pholas, these Saxicavæ habitually break into one
another’s houses, as we see here, and even cut one another’s shells and
bodies through and through most ruthlessly. They will live very well
out of the rock, and may be kept a considerable time in the aquarium.
There is no doubt that the burrowing Mollusca are slowly but surely
effecting changes in the configuration of rocky coasts, by destroying
the rock. It is true their excavations extend but a few inches in
depth; but then, as the force of the elements readily breaks down the
thin partitions left standing, and discovers a new face, so the borers
are continually renewing their attacks on this; and so in time the
cliffs are worn away, while the debris of impalpable mud is deposited
upon the shallows, entering into new combinations, and filling up
estuaries and harbours.