the Continent, and made their abode here. It is curious to note that the
migratory birds when returning to France and Italy, and thence to the
sunny regions of Algiers and other parts of Northern Africa, always
cross the seas where in remote ages there was dry land. They always
traverse the same route; and it appears that the recollection of the
places where their ancestors crossed has been preserved by them through
all the centuries that have elapsed since "the silver streak" was formed
that severs England from her neighbours.

In the times of which we are speaking the land was much higher than it
is now. Snowdon was 600 feet greater, and the climate was much colder
and more rigorous. Glaciers like those in Switzerland were in all the
higher valleys, and the marks of the action of the ice are still plainly
seen on the rocky cliffs that border many a ravine. Moreover we find in
the valleys many detached rocks, immense boulders, the nature of which
is quite different from the character of the stone in the neighbourhood.
These were carried down by the glaciers from higher elevations, and
deposited, when the ice melted, in the lower valleys. Hence in this
glacial period the condition of the country was very different from what
it is now.

Then a remarkable change took place. The land began to sink, and its
elevation so much decreased that the central part of the country became
a huge lake, and the peak of Snowdon was an island surrounded by the sea
which washed with its waves the lofty shoulder of the mountain. This is
the reason why shells and shingle are found in high elevations. The Ice
Age passed away and the climate became warmer. The Gulf Stream found its
way to our shores, and the country was covered by a warm ocean having
islands raising their heads above the surface. Sharks swam around, whose
teeth we find now buried in beds of clay. The land continued to rise,