st slates are found, this rule,
I believe, stands true.

It stands true, certainly, of the ancient Silurian rocks of Wales,
Cumberland, Ireland, and Scotland.

For, throughout great tracts of Russia, and in parts of Norway and
Sweden, Sir Roderick Murchison discovered our own Silurian beds,
recognisable from their peculiar fossils. But in what state? Not
contracted, upheaved, and hardened to slates and grits, as they are
in Wales and elsewhere: but horizontal, unbroken, and still soft,
because undisturbed by volcanic rooks and earthquakes. At the bottom
of them all, near Petersburg, Sir Roderick found a shale of dried mud
(to quote his own words), "so soft and incoherent that it is even
used by sculptors for modelling, although it underlies the great mass
of fossil-bearing Silurian rocks, and is, therefore, of the same age
as the lower crystalline hard slates of North Wales. So entirely
have most of these eldest rocks in Russia been exempted from the
influence of change, throughout those enormous periods which have
passed away since their accumulation."

Among the many discoveries which science owes to that illustrious
veteran, I know none more valuable for its bearing on the whole
question of the making of the earth-crust, than this one magnificent
fact.

But what a contrast between these Scandinavian and Russian rocks and
those of Britain! Never exceeding, in Scandinavia, a thousand feet
in thickness, and lying usually horizontal, as they were first laid
down, they are swelled in Britain to a thickness of thirty thousand
feet, by intruded lavas and ashes; snapt, turned, set on end at every
conceivable angle; shifted against each other to such an extent,
that, to give a single instance, in the Vale of Gwynnant, under
Snowdon, an immense wedge of porphyry has been thrust up, in what is
now the bottom of the valley, between rocks far newer than it, on one
side to a height of eight hundred, on the other to a height of
eighteen hundred feet--half the present height of Snowdon. Nay, the
very slate beds of Snowdonia have not forced their way up from under
the mountain--without long and fearful struggles. They are set in
places upright on end, then horizontal again, then sunk in an
opposite direction, then curled like sea-waves, then set nearly
upright once more, and faulted through and through, six times, I
believe, in the distance of a mile or two; they carry here and there
o