That is a general rule among all geologists, and not
to be gainsaid.
Now I think I may say, that, granting that we can recognise a bed by
its fossils, there are few or no beds which are found in one place
upheaved, broken, and altered by heat, which are not found in some
other place still horizontal, unbroken, unaltered, and more or less
as they were at first.
From the most recent beds; from the upheaved coral-rocks of the West
Indies, and the upheaved and faulted boulder clay and chalk of the
Isle of Moen in Denmark--downwards through all the strata, down to
that very ancient one in which the best 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.
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