estion not yet answered. I believe the former
theory to be the true one. That there was life, in the sea at least,
even before the oldest Cambrian rocks were laid down, is proved by
the discovery of the now famous fossil, the Eozoon, in the Laurentian
limestones, which seems to have grown layer after layer, and to have
formed reefs of limestone as do the living coral-building polypes.
We know no more as yet. But all that we do know points downwards,
downwards still, warning us that we must dig deeper than we have dug
as yet, before we reach the graves of the first living things.

Let this suffice at present for the Cambrian and Laurentian rocks.

The Silurian rocks, lower and upper, which in these islands have
their chief development in Wales, and which are nearly thirty-eight
thousand feet thick; and the Devonian or Old Red sandstone beds,
which in the Fans of Brecon and Carmarthenshire attain a thickness of
ten thousand feet, must be passed through in an upward direction
before we reach the bottom of that Carboniferous Limestone of which I
spoke in my last paper. We thus find on the Cambrian rocks forty-
five thousand feet at least of newer rocks, in several cases lying
unconformably on each other, showing thereby that the lower beds had
been upheaved, and their edges worn off on a sea-shore, ere the upper
were laid down on them; and throughout this vast thickness of rocks,
the remains of hundreds of forms of animals, corals, shells, fish,
older forms dying out in the newer rocks, and new ones taking their
places in a steady succession of ever-varying forms, till those in
the upper beds have become unlike those in the lower, and all are
from the beginning more or less unlike any existing now on earth.
Whole families, indeed, disappear entirely, like the Trilobites,
which seem to have swarmed in the Silurian seas, holding the same
place there as crabs and shrimps do in our modern seas. They vanish
after the period of the coal, and their place is taken by an allied
family of Crustaceans, of which only one form (as far as I am aware)
lingers now on earth, namely, the "King Crab," or Limulus, of the
Indian Seas, a well-known animal, of which specimens may sometimes be
seen alive in English aquaria. So perished in the lapse of those
same ages, the armour-plated or "Ganoid" fish which Hugh Miller made
so justly famous--and which made him so justly famous in return--
appearing first i