A Manual of Elementary Geology: or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological MonumentsLyell, Charles, Sir
Science
A Manual of Elementary Geology: or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological Monuments
Lyell, Charles, Sir
Geology
corroded still more deeply at points lower down where they are just reached
by the breakers. By this action the stone acquires a wrinkled and furrowed
outline, and very near the sea it becomes rough and branching, as if
covered with corals. Such effects are traced not only on the present shore,
but at the base of the ancient cliffs far in the interior. Lastly, it
remains only to speak of the terraces, which extend with a gentle slope
from the base of almost all the inland cliffs, and are for the most part
narrow where the rock is hard, but sometimes half a mile or more in breadth
where it is soft. They are the effects of the encroachment of the ancient
sea upon the shore at those levels at which the land remained for a long
time stationary. The justness of this view is apparent on examining the
shape of the modern shore wherever the sea is advancing upon the land, and
removing annually small portions of undermined rock. By this agency a
submarine platform is produced on which we may walk for some distance from
the beach in shallow water, the increase of depth being very gradual, until
we reach a point where the bottom plunges down suddenly. This platform is
widened with more or less rapidity according to the hardness of the rocks,
and when upraised it constitutes an inland terrace.
But the four principal lines of cliff observed in the Morea do not imply,
as some have imagined, four great eras of sudden upheaval; they simply
indicate the intermittence of the upheaving force. Had the rise of the land
been continuous and uninterrupted, there would have been no one prominent
line of cliff; for every portion of the surface having been, in its turn,
and for an equal period of time, a sea-shore, would have presented a nearly
similar aspect. But if pauses occur in the process of upheaval, the waves
and currents have time to sap, throw down, and clear away considerable
masses of rock, and to shape out at certain levels lofty ranges of cliffs
with broad terraces at their base.
There are some levelled spaces, however, both ancient and modern, in the
Morea, which are not due to denudation, although resembling in outline
the terraces above described. They may be called Terraces of Deposition,
since they have resulted from the gain of land upon the sea where rivers
and torrents have produced deltas. If the sedimentary matter has filled
up a bay or gulf surrounded by steep mountains, a flat plain is formed
skirting the inland precipices; and if these deposits are upraised,
they form a feature in the landscape very similar to the areas of
denudation before described.
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