"
To them belong the Llandeilo flags and slates of Wales, and the
Skiddaw slates of Cumberland, amid beds abounding in extinct fossil
forms. Fossil shells are found, it is true, in the upper Cambrian
beds. In the lower they have all but disappeared. Whether their
traces have been obliterated by heat and pressure, and chemical
action, during long ages; or whether, in these lower beds, we are
actually reaching that "Primordial Zone" conceived of by M. Barrande,
namely, rocks which existed before living things had begun to people
this planet, is a question 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.
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