n vast profusion, are
considered to have this good effect; and it is indeed impossible that
the sheep can browse on the short grass of the places just mentioned,
without devouring a prodigious quantity of them, especially in the
night, or after rain, when the Bulimi and Helices ascend the stunted
blades. "The sweetest mutton," says Borlase, "is reckoned to be that
of the smallest sheep, which feed on the commons where the sands are
scarce covered with the green sod, and the grass exceedingly short; such
are the towens or sand hillocks in Piran Sand, Gwythien, Philac, and
Senangreen, near the Land's End, and elsewhere in like situations. From
these sands come forth snails of the turbinated kind, but of different
species, and all sizes from the adult to the smallest just from the egg;
these spread themselves over the plains early in the morning, and,
whilst they are in quest of their own food among the dews, yield a most
fattening nourishment to the sheep." (_Hist. of Cornwall_.)

Among birds the shell-fish have many enemies. Several of the duck and
gull tribes, as you might anticipate, derive at least a portion of their
subsistence from them. The pied oyster-catcher receives its name from
the circumstance of feeding on oysters and limpets, and its bill is so
well adapted to the purpose of forcing asunder the valves of the one,
and of raising the other from the rock, that "the Author of Nature,"
as Derham says, "seems to have framed it purely for that use." Several
kinds of crows likewise prey upon shell-fish, and the manner in which
they force the strong hold of their victims is very remarkable. A friend
of Dr. Darwin's saw above a hundred crows on the northern coast of
Ireland, at once, preying upon muscles. Each crow took a muscle up in
the air twenty or forty yards high, and let it fall on the stones, and
thus broke the shell. Many authorities might be adduced in corroboration
of this statement. In Southern Africa so many of the Testacea are
consumed by these and other birds, as to have given rise to an opinion
that the marine shells found buried in the distant plains, or in the
sides of the mountains, have been carried there by their agency, and
not, as generally supposed, by eruptions of the sea. Mr. Barrow, who
is of this opinion, tells us, in confirmation of it, that "there is
scarcely a sheltered cavern in the sides of the mountains that arise
immediately from the sea, where living shell-fish may not be found any