1_5o'
THE SEAS . .
made of calcareous matter but this is protected from the '
action of theacid, as‘ we have seen, by the Covering of horny
matter.
The acid-producing gland is'not present in closely
'
related mussels whichdo not bore into rock.
The borings
of the Date—mussel have proved of great value in a somewhat
unexpected connection, that of earth movements.
The
classic example is the borings in the limestone pillars of the
Temple of Seraphis at, Pozzuoli near Naples.
These pillars
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are
to.—day some distance above sea level, but for some
distance upwards are perforated with the burrows of the
’
Date-mussel.
Since the temple must originally have been.
.
built above sea level, it is clear that the land sank until
the pillars were covered at least to the extent to which
.
they have been burrowed into.
It is just as obvious that
_
since that time the land has risen again «so that the temple
is once more on dry land.
Thus the presence of the h01es
made by the Date-mussel enables us to prove
'
land in the neighbourhood of*Pozzuoli has both sunk and
risen again within historic time.
Crustaceans do far less damage to stone than ,to wood.
Both limest0ne and. coral are bored into to a slight extent -
by certain barnacles,. but the only Crustacean which does
,
much damage—is another-species of ' the Sphæroma which
bores in
This creature can only workÎin soft sand—
stone or clayst0ne but has
conSiderable damage in
_
New Zealand by destrOying harbour works made of the
.
latter material.
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"
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The rock—boring animals cannot obtain any food ‘ fr0m
.
the rock;
they make their burrows and live in them
purely on account of,th‘e shelter with Which they are provided.
'The borrows‘ are never long and the animals are
in free communication with the water outside andffom
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which they take their food which in all-cases consists of
.
ne particles or microScopic animals and plants.‘
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In general.