an inclined surface, thickly capped by well-rounded pebbles of about the
same size, would be ultimately left. (On the eastern side of Chiloe, which
island we shall see in the next chapter is now rising, I observed that all
the beaches and extensive tidal-flats were formed of shingle.) On the
gravel now accumulating, the waves, aided by the wind, sometimes throw up a
thin covering of sand, together with the common coast-shells. Shells thus
cast up by gales, would, during an elevatory period, never again be touched
by the sea. Hence, on this view of a slow and gradual rising of the land,
interrupted by periods of rest and denudation, we can understand the
pebbles being of about the same size over the entire width of the step-like
plains,--the occasional thin covering of sandy earth,--and the presence of
broken, unrolled fragments of those shells, which now live exclusively near
the coast.

SUMMARY OF RESULTS.

It may be concluded that the coast on this side of the continent, for a
space of at least 1,180 miles, has been elevated to a height of 100 feet in
La Plata, and of 400 feet in Southern Patagonia, within the period of
existing shells, but not of existing mammifers. That in La Plata the
elevation has been very slowly effected: that in Patagonia the movement may
have been by considerable starts, but much more probably slow and quiet. In
either case, there have been long intervening periods of comparative rest,
during which the sea corroded deeply, as it is still corroding, into the
land. (I say COMPARATIVE and not ABSOLUTE rest, because the sea acts, as we
have seen, with great denuding power on this whole line of coast; and
therefore, during an elevation of the land, if excessively slow (and of
course during a subsidence of the land), it is quite possible that lines of
cliff might be formed.) That the periods of denudation and elevation were
contemporaneous and equable over great spaces of coast, as shown by the