t too carefully bear in mind the laws which
regulate the production of men, and also the body of evidence which
proves that the crust of the earth is not motionless, but rising in one
place and sinking in another. The grand invasions of Europe by Asiatic
hordes have been much more violent and abrupt than would answer to a
steady pressure resulting from overpopulation, and too extensive for
mere warlike incitement; they answer more completely to the experience
of some irresistible necessity arising from an insuperable physical
cause, which could drive in hopeless despair from their homes the young
and the old, the vigorous and feeble, with their cattle, and waggons,
and flocks. Such a cause is the shifting of the soil and disturbance of
the courses of water. The tribes compelled to migrate were forced along
the path-zone, their track being, therefore, on a parallel of latitude,
and not on a meridian; and hence, for the reasons set forth in the
preceding chapter, their movements and journey of easier accomplishment.

[Sidenote: Rate and extent of these movements.]

These geological changes then enter as an element in human history, not
only for Asia, of which the great inland sea has dwindled away to the
Caspian, and lost its connection with the Baltic, but for Europe also.
The traditions of ancient deluges, which are the primitive facts of
Greek history, refer to such movements, perhaps the opening of the
Thracian Bosphorus was one of them. In much later times we are
perpetually meeting with incidents depending on geological disturbances;
the caravan trade of Asia Minor was destroyed by changes of level and
the accumulation of sands blown from the encroaching deserts; the Cimbri
were impelled into Italy by the invasion of the sea on their
possessions. There is not a shore in Europe which does not give similar
evidence; the mouths of the Rhine, as they were in the Roman times, are
obliterated; the eastern coast of England has been cut away for miles.
In the Mediterranean the shore-line is altogether changed; towns, once
on the coast, are far away inland; others have sunk beneath the sea.
Islands, like Rhodes, have risen from the bottom. The North Adriatic,
once a deep gulf, has now become shallow; there are leaning towers and
inclining temples that have sunk with the settling of the earth. On the
opposite extremity of Europe, the Scandinavian peninsula furnishes an
instance of slow secular motion, the northern part rising