We should not forget
that only a small portion of the world is known with accuracy. M.
Barrande has lately added another and lower stage to the Silurian
system, abounding with new and peculiar species. Traces of life have
been detected in the Longmynd beds beneath Barrande's so-called
primordial zone. The presence of phosphatic nodules and bituminous
matter in some of the lowest azoic rocks, probably indicates the
former existence of life at these periods. But the difficulty of
understanding the absence of vast piles of fossiliferous strata, which
on my theory no doubt were somewhere accumulated before the Silurian
epoch, is very great. If these most ancient beds had been wholly worn
away by denudation, or obliterated by metamorphic action, we ought to
find only small remnants of the formations next succeeding them in
age, and these ought to be very generally in a metamorphosed
condition. But the descriptions which we now possess of the Silurian
deposits over immense territories in Russia and in North America, do
not support the view, that the older a formation is, the more it has
suffered the extremity of denudation and metamorphism.
The case at present must remain inexplicable; and may be truly urged
as a valid argument against the views here entertained. To show that
it may hereafter receive some explanation, I will give the following
hypothesis. From the nature of the organic remains, which do not
appear to have inhabited profound depths, in the several formations of
Europe and of the United States; and from the amount of sediment,
miles in thickness, of which the formations are composed, we may infer
that from first to last large islands or tracts of land, whence the
sediment was derived, occurred in the neighbourhood of the existing
continents of Europe and North America.
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