came that neither the terraces nor the upper nor lower edges of the
escarpments were horizontal. Along lines of coast, even of great lengths,
such as that of Patagonia, if they are nearly uniformly exposed, the
corroding power of the waves will be checked and conquered by the elevatory
movement, as often as it recommences, at about the same period; and hence
the terraces, or accumulated beach-lines, will commence being formed at
nearly the same levels: at each succeeding period of rest, they will, also,
be eaten into at nearly the same rate, and consequently there will be a
much closer coincidence in their levels and inclinations, than in the
terraces and escarpments formed round bays with their different parts very
differently exposed to the action of the sea. It is only where the waves
are enabled, after a long lapse of time, slowly to corrode hard rocks, or
to throw up, owing to the supply of sediment being small and to the surface
being steeply inclined, a narrow beach or mound, that we can expect, as at
Glen Roy in Scotland ("Philosophical Transactions" 1839 page 39.), a
distinct line marking an old sea-level, and which will be strictly
horizontal, if the subsequent elevatory movements have been so: for in
these cases no discernible effects will be produced, except during the long
intervening periods of rest; whereas in the case of step-formed coasts,
such as those described in this and the preceding chapter, the terraces
themselves are accumulated during the slow elevatory process, the
accumulation commencing sooner in protected than in exposed situations, and
sooner where there is copious supply of detritus than where there is
little; on the other hand, the steps or escarpments are formed during the
stationary periods, and are more deeply cut down and into the coast-land in
exposed than in protected situations;--the cutting action, moreover, being
prolonged in the most exposed parts, both during the beginning and ending,
if slow, of the upward movement.

Although in the foregoing discussion I have assumed the elevation to have