ose found at Geize_. This
place is supposed to be about twenty miles from the sea; and is one
instance, among many in Caithness, of _the ocean's covering the inland
country at some former period of time_."

The state of keeping in which the boulder-shells of Caithness occur is
exactly what, on the iceberg theory, might be premised. The ponderous
ice-rafts that went grating over the deep-sea bottom, grinding down its
rocks into clay, and deeply furrowing its pebbles, must have borne
heavily on its comparatively fragile shells. If rocks and pebbles did
not escape, the shells must have fared but hardly. And very hardly they
have fared: the rather unpleasant casualty of being crushed to death
must have been a greatly more common one in those days than in even the
present age of railways and machinery. The reader, by passing half a
bushel of the common shells of our shores through a barley-mill, as a
preliminary operation in the process, and by next subjecting the broken
fragments thus obtained to the attritive influence of the waves on some
storm-beaten beach for a twelvemonth or two, as a finishing operation,
may produce, when he pleases, exactly such a water-worn shelly debris as
mottles the blue boulder-clays of Caithness. The proportion borne by the
fragments of one species of shell to that of all the others is very
extraordinary. The _Cyprina islandica_ is still by no means a rare
mollusc on our Scottish shores, and may, on an exposed coast, after a
storm, be picked up by dozens, attached to the roots of the deep-sea
tangle. It is greatly less abundant, however, than such shells as
_Purpura lapillus_, _Mytilus edule_, _Cardium edule_, _Littorina
littorea_, and several others; whereas in the boulder-clay it is, in the
proportion of at least ten to one, more abundant than all the others put
together. The great strength of the shell, however, may have in part led
to this result; as I find that its stronger and massier portions,--those
of the umbo and hinge-joint,--are exceedingly numerous in proportion to
its slimmer and weaker fragments. "The _Cyprina islandica_," says Dr.
Fleming, in his "British Animals," "is the largest British bivalve
shell, measuring sometimes thirteen inches in circumference, and,
exclusively of the animal, weighing upwards of nine ounces." Now, in a
collection of fragments of Cyprina sent me by Mr. Dick, disinterred from
the boulder-clay in various localities in the neighborhood of Thurso,
and wei