he
several formations {290} being separated from each other by wide intervals
of time. When we see the formations tabulated in written works, or when we
follow them in nature, it is difficult to avoid believing that they are
closely consecutive. But we know, for instance, from Sir R. Murchison's
great work on Russia, what wide gaps there are in that country between the
superimposed formations; so it is in North America, and in many other parts
of the world. The most skilful geologist, if his attention had been
exclusively confined to these large territories, would never have suspected
that during the periods which were blank and barren in his own country,
great piles of sediment, charged with new and peculiar forms of life, had
elsewhere been accumulated. And if in each separate territory, hardly any
idea can be formed of the length of time which has elapsed between the
consecutive formations, we may infer that this could nowhere be
ascertained. The frequent and great changes in the mineralogical
composition of consecutive formations, generally implying great changes in
the geography of the surrounding lands, whence the sediment has been
derived, accords with the belief of vast intervals of time having elapsed
between each formation.

But we can, I think, see why the geological formations of each region are
almost invariably intermittent; that is, have not followed each other in
close sequence. Scarcely any fact struck me more when examining many
hundred miles of the South American coasts, which have been upraised
several hundred feet within the recent period, than the absence of any
recent deposits sufficiently extensive to last for even a short geological
period. Along the whole west coast, which is inhabited by a peculiar marine
fauna, tertiary beds are so poorly developed, that no record of several
{291} successive and peculiar marine faunas will probably be preserved to a
distant age. A little reflection will explain why along the rising coast of
the western side of South America, no extensive formations with recent or
tertiary remains can anywhere be found, though the supply of sediment must
for ages have been great, from the enormous degradation of the coast-rocks
and from muddy streams entering the sea. The explanation, no doubt, is,
that the littoral and sub-littoral deposits are continually worn away, as
soon as they are brought up by the slow and gradual rising of the land
within the grinding action of the coa