the
shore line; _p_, _p_, the pivotal points; _l_, _s_, the sea line. In
diagram III, the curved line designates a shore; the line _a b_,
connecting the pivotal points _p_, _p_, is partly under the land and
partly under the sea.]

It is easy to see that if the sea floors tend to sink downward, while
the continental lands uprise, the movements which take place may be
compared with those which occur in a lever about a fulcrum point. In
this case the sea end of the bar is descending and the land end
ascending. Now, it is evident that the fulcrum point may fall to the
seaward or to the landward of the shore; only by chance and here and
there would it lie exactly at the coast line. By reference to the
diagram (Fig. 8), it will be seen that, while the point of rotation is
just at the shore, a considerable movement may take place without
altering the position of the coast line. Where the point of no
movement is inland of the coast, the sea will gain on the continent;
where, however, the point is to seaward, beneath the water, the land
will gain on the ocean. In this way we can, in part at least, account
for the endless changes in the attitude of the land along the coastal
belt without having to suppose that the continents cease to rise or
the sea floors to sink downward. It is evident that the bar or section
of the rocks from the interior of the land to the bottoms of the seas
is not rigid; it is also probable that the matter in the depths of the
earth, which moves with the motions of this bar, would change the
position of the fulcrum point from time to time. Thus it may well come
about that our coast lines are swaying up and down in ceaseless
variation.

In very recent geological times, probably since the beginning of the
last Glacial period, the region about the Dismal Swamp in Virginia has
swayed up and down through four alternating movements to the extent of
from fifty to one hundred feet. The coast of New Jersey is now sinking
at the rate of about two feet in a hundred years. The coast of New
England, though recently elevated to the extent of a hundred feet or
more, at a yet later time sank down, so that at some score of points
between New York and Eastport, Me., we find the remains of forests
with the roots of their trees still standing below high-tide mark in
positions where the trees could not have grown. Along all the marine
coasts of the world which have been carefully studied from this point
of view there are si