secutive formations, generally implying great changes in the
geography of the surrounding lands, whence the sediment was derived,
accord with the belief of vast intervals of time having elapsed between
each formation.

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 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 the 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 coast-waves.

We may, I think, conclude that sediment must be accumulated in extremely
thick, solid, or extensive masses, in order to withstand the incessant
action of the waves, when first upraised and during subsequent
oscillations of level, as well as the subsequent subaerial degradation.
Such thick and extensive accumulations of sediment may be formed in two
ways; either in profound depths of the sea, in which case the bottom
will not be inhabited by so many and such varied forms of life as the
more shallow seas; and the mass when upraised will give an imperfect
record of the organisms which existed in the neighbourhood during
the period of its accumulation. Or sediment may be deposited to any
thickness and extent over a shallow bottom, if it continue slowly to
subside. In this latter case, as long as the rate of subsidence and
supply of sediment nearly balance each other, the sea will remain
shallow and favourable for many and varied forms, and thus a rich
fossiliferous formation, thick enough, when upraised, to resist a la