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
extensive sylvan regions, it is thought that the vegetation, the rubbish
of decayed forests, was carried by rivers into estuaries, and there
accumulated into vast natural rafts, until it sank to the bottom, where
an overlayer of sand or mud would prepare it for becoming a stratum of
coal. Others conceive that the vegetation first went into the condition
of peat moss, that a sink in a level then exposed it to be overrun by
the sea and covered with a layer of sand or mud; that a subsequent
uprise made the mud dry land, and fitted it to bear a new forest, which
afterwards, like its predecessors, became a bed of peat--that, in short,
by repetitions of this process the alternate layers of coal, sand and
shell constituting the carboniferous group were formed.

The _Magnesian Limestone_ deposits succeed the carboniferous, and
sometimes pass into them by insensible gradations. In the south of
England they are represented by conglomerates, and partly composed of
the solid and more or less rounded fragments of the older strata. They
afford a proof of what geologists have often occasion to remark of the
long periods of time during which the ancient works of nature were
perfected; for the older rocks were solid as they are now, and their
organic remains petrified at the time these conglomerates were forming.

We can only briefly glance at the remaining chapters of geological
history. The _New Red Sandstone_ form