lding and making
lime. In a quarry on the N. W. side of the island, about 100 yards from
the sea, some fossil eggs of turtles have been discovered in the hard
rock thus formed. The eggs must have been nearly hatched at the time
when they perished; for the bones of the young turtle are seen in the
interior, with their shape fully developed, the interstices between the
bones being entirely filled with grains of sand, which are cemented
together, so that when the egg-shells are removed perfect casts of their
form remain in stone. In the single specimen here figured (fig. 106),
which is only five inches in its longest diameter, no less than seven
eggs are preserved.[1110]

To explain the state in which they occur fossil, it seems necessary to
suppose that after the eggs were almost hatched in the warm sand, a
great wave threw upon them so much more sand as to prevent the rays of
the sun from penetrating, so that the yolk was chilled and deprived of
vitality. The shells were, perhaps, slightly broken at the same time,
so that small grains of sand might gradually be introduced into the
interior by water as it percolated through the beach.

[Illustration: Fig. 107.

One of the eggs in fig. 106, of the natural size, showing the bones of
the foetus which had been nearly hatched.]

_Marine testacea._--The aquatic animals and plants which inhabit an
estuary are liable, like the trees and land animals which people the
alluvial plains of a great river, to be swept from time to time far into
the deep; for as a river is perpetually shifting its course, and
undermining a portion of its banks with the forests which cover them, so
the marine current alters its direction from time to time, and bears
away the banks of sand and mud against which it turns its force. These
banks may consist in great measure of shells peculiar to shallow and
sometimes brackish water, which may have been accumulating for
centuries, until at length they are carried away and spread out along
the bottom of the sea, at a depth at which they could not have lived and
multiplied. Thus littoral and estuary shells are more frequently liable
even than freshwater species, to be intermixed with the exuviae of
pelagic tribes.

After the storm of February 4, 1831, when several vessels were wrecked
in the estuary of the Forth, the current was directed against a bed of
oysters with such force, that great heaps of them were thrown _alive_
upon the beach, and remained abov