e years; at Luleo,[730] no less than a mile in twenty-eight
years; facts which might all be admitted consistently with the
assumption that the level of the Baltic has remained unchanged, like
that of the Adriatic, during a period when the plains of the Po and the
Adige have greatly extended their area.

It was also alleged that certain insular rocks, once entirely covered
with water, had at length protruded themselves above the waves, and
grown, in the course of a century and a half, to be eight feet high. The
following attempt was made to explain away this phenomenon:--In the
Baltic, large erratic blocks, as well as sand and smaller stones which
lie on shoals, are liable every year to be frozen into the ice, where
the sea freezes to the depth of five or six feet. On the melting of the
snow in spring, when the sea rises about half a fathom, numerous
ice-islands float away, bearing up these rocky fragments so as to convey
them to a distance; and if they are driven by the waves upon shoals,
they may convert them into islands by depositing the blocks; if stranded
upon low islands, they may considerably augment their height.

Browallius, also, and some other Swedish naturalists, affirmed that some
islands were lower than formerly; and that, by reference to this kind of
evidence, there was equally good reason for contending that the level of
the Baltic was gradually rising. They also added another curious proof
of the permanency of the water level, at some points at least, for many
centuries. On the Finland coast were some large pines, growing close to
the water's edge; these were cut down, and, by counting the concentric
rings of annual growth, as seen in a transverse section of the trunk, it
was demonstrated that they had stood there for four hundred years. Now,
according to the Celsian hypothesis, the sea had sunk about fifteen feet
during that period, in which case the germination and early growth of
these pines must have been, for many seasons, below the level of the
water. In like manner it was asserted, that the lower walls of many
ancient castles, such as those of Sonderburg and Abo, reached then to
the water's edge, and must, therefore, according to the theory of
Celsius, have been originally constructed below the level of the sea.

[Illustration: Fig. 91.]

In reply to this last argument, Colonel Hallstrom, a Swedish engineer,
well acquainted with the Finland coast, assured me, that the base of the
walls of the