The _Old Red Sandstone, or Devonian System_, comes next. It forms the
material of the grand and rugged mountains which fringe many parts of
our Highland coasts, and ranges, on the south flank of the Grampians,
from the eastern to the western sea of Scotland. There is no part of
geology and science more clear than that which refers to the ages of
mountains. It is as certain that the Grampian mountains are older than
the Alps and Apennines, as it is that civilisation had reached Italy and
enabled her to subdue the world, while Scotland was the abode of
barbarism. The Pyrenees, Carpathians, and other ranges of continental
Europe are all younger than these Scotch hills, or even the
insignificant Mendip Hills of southern England. Stratification tells
this tale as plainly, and more truly, than LIVY tells the story of the
Roman republic. It tells us that at the time when the Grampians sent
streams and detritus to straits where now the valleys of the Forth and
Clyde meet, the greater part of Europe was a wide ocean.

The last three series of strata contain the remains of the earliest
occupants of the globe, and of which we shall soon speak. They are of
enormous thickness--in England, not much less than 30,000 feet, or
nearly six miles.

We have now arrived at the secondary rocks, of which the lowest group is
the _Carboniferous Formation_, so called from its remarkable feature of
numerous interspersed beds of coal. It commences with beds of the
mountain limestone, which in England attains a depth of 800 yards. Coal
is altogether composed of the matter of a terrestrial vegetation,
transmuted by putrefaction of a peculiar kind beneath the surface of
water, and in the absence of air. From examples seen at the present day
at the mouths of such rivers as the Mississippi, which traverse