flow down
every slope. Messrs. Ramsay and Whitaker have shown, and the observation
is a most striking one, that the great lines of escarpment in the
Wealden district and those ranging across England, which formerly were
looked at as ancient sea-coasts, cannot have been thus formed, for each
line is composed of one and the same formation, while our sea-cliffs are
everywhere formed by the intersection of various formations. This being
the case, we are compelled to admit that the escarpments owe their
origin in chief part to the rocks of which they are composed, having
resisted subaerial denudation better than the surrounding surface;
this surface consequently has been gradually lowered, with the lines of
harder rock left projecting. Nothing impresses the mind with the vast
duration of time, according to our ideas of time, more forcibly than the
conviction thus gained that subaerial agencies, which apparently have
so little power, and which seem to work so slowly, have produced great
results.

When thus impressed with the slow rate at which the land is worn
away through subaerial and littoral action, it is good, in order to
appreciate the past duration of time, to consider, on the one hand, the
masses of rock which have been removed over many extensive areas, and on
the other hand the thickness of our sedimentary formations. I remember
having been much struck when viewing volcanic islands, which have been
worn by the waves and pared all round into perpendicular cliffs of
one or two thousand feet in height; for the gentle slope of the
lava-streams, due to their formerly liquid state, showed at a glance how
far the hard, rocky beds had once extended into the open ocean. The same
story is told still more plainly by faults--those great cracks along
which the strata have been upheaved on one side, or thrown down on the
other, to the height or depth of thousands of feet; for since the crust
cracked, and it makes no great difference whether the upheaval was
sudden, or, as most geologists now believe, was slow and effected by
many starts, the surface of the land has been so completely planed down
that no trace of these vast dislocations is externally visible. The
Craven fault, for instance, extends for upward of thirty miles, and
along this line the vertical displacement of the strata varies from 600
to 3,000 feet. Professor Ramsay has published an account of a downthrow
in Anglesea of 2,300 feet; and he informs me that he fully