t, whatever names be selected as most appropriate or
descriptive for these divisions, geologists should agree to use them in
the same sense.

There is one other geological term, bequeathed to us by a great authority,
and which cannot be changed for the better: I mean that of Geological
Horizon, applied by Humboldt to the whole extent of any one geological
division,--as, for instance, the Silurian horizon, including the whole
extent of the Silurian epoch. It indicates one level in time, as the
horizon which limits our view indicates the farthest extension of the
plain on which we stand in space.

* * * * *

We left America at the close of the Carboniferous epoch, when the central
part of the United States was already raised above the water. Let us now
give a glance at Europe in those early days, and see how far her physical
history has advanced. What European countries loom up for us out of the
Azoic sea, corresponding in time and character to the low range of hills
which first defined the northern boundary of the United States? what did
the Silurian and Devonian epochs add to these earliest tracts of dry land
in the Old World? and where do we find the coal basins which show us the
sites of her Carboniferous forests? Since the relation between the epochs
of comparative tranquillity and the successive upheavals has been so
carefully traced in Europe, I will endeavor, while giving a sketch of that
early European world, to point out, at the same time, the connection of
the different systems of upheaval with the successive stratified deposits,
without, however, entering into such details as must necessarily become
technical and tedious.

In the European ocean of the Azoic epoch we find five islands of
considerable size. The largest of these is at the North. Scandinavia had
even then almost her present outlines; for Norway, Sweden, Finland, and
Lapland, all of which are chiefly granitic in character, were among the
first lands to be raised. Between Sweden and Norway, there is, however,
still a large tract of land under water, forming an extensive lake or a
large inland sea in the heart of the country. If the reader will take the
trouble to look on any geological map of Europe, he will see an extensive
patch of Silurian rock in the centre of Sweden and Norway. This represents
that sheet of water gradually to be filled by the accumulation of Silurian
deposits and afterwards raised by a later di