obable. He ought also to have symptom e, and so forth;
and as I find successively each of these symptoms which are proper to
A, my first guess will become more and more probable, till it reaches
practical certainty.

Now let us do the same, and say--If this strange dream be true, and
the lowlands of the North were once under an icy sea, ought we not to
find sea-shells in their sands and clays? Not abundantly, of course.
We can understand that the sea-animals would be too rapidly covered
up in mud, and too much disturbed by icebergs and boulders, to be
very abundant. But still, some should surely be found here and
there.

Doubtless; and if my northern-town readers will search the boulder-
clay pits near them, they will most probably find a few shells, if
not in the clay itself, yet in sand-beds mixed with them, and
probably underlying them. And this is a notable fact, that the more
species of shells they find, the more they will find--if they work
out their names from any good book of conchology--of a northern type;
of shells which notoriously, at this day, inhabit the colder seas.

It is impossible for me here to enter at length on a subject on which
a whole literature has been already written. Those who wish to study
it may find all that they need know, and more, in Lyell's "Student's
Elements of Geology," and in chapter xii. of his "Antiquity of Man."
They will find that if the evidence of scientific conchologists be
worth anything, the period can be pointed out in the strata, though
not of course in time, at which these seas began to grow colder, and
southern and Mediterranean shells to disappear, their places being
taken by shells of a temperate, and at last of an Arctic climate;
which last have since retreated either toward their native North, or
into cold water at great depths. From Essex across to Wales, from
Wales to the aestuary of the Clyde, this fact has been verified again
and again. And in the search for these shells, a fresh fact, and a
most startling one, was discovered. They are to be found not only in
the clay of the lowlands, but at considerable heights up the hills,
showing that, at some time or other, these hills have been submerged
beneath the sea.

Let me give one example, which any tourist into Wales may see for
himself. Moel Tryfaen is a mountain over Carnarvon. Now perched on
the side of that mountain, fourteen hundred feet above the present
sea-