inking down. These movements are attested by
the position of the old shore lines formed during the later stages of
the Glacial epoch. Thus around Lake Ontario, as well as the other
Great Lakes, the beaches which mark the higher positions of those
inland seas during the closing stages of the ice time, and which, of
course, were when formed horizontal, now rise to the northward at the
rate of from two to five feet for each mile of distance. Recent
studies by Mr. G.K. Gilbert show that this movement is still in
progress.

Other evidence going to show the extent to which the movements of the
earth's crust are affected by the weight of materials are found in the
fact that wherever along the shores thick deposits of sediments are
accumulated the tendency of the region where they lie is gradually to
sink downward, so that strata having an aggregate thickness of ten
thousand feet or more may be accumulated in a sea which was always
shallow. The ocean floor, in general, is the part of the earth's
surface where strata are constantly being laid down. In the great
reservoir of the waters the _debris_ washed from the land, the dust
from volcanoes, and that from the stellar spaces, along with the vast
accumulation of organic remains, almost everywhere lead to the
steadfast accumulation of sedimentary deposits. On the other hand, the
realms of the surface above the ocean level are constantly being worn
away by the action of the rivers and glaciers, of the waves which beat
against the shores, and of the winds which blow over desert regions.
The result is that the lands are wearing down at the geologically
rapid average rate of somewhere about one foot in five thousand years.
All this heavy matter goes to the sea bottoms. Probably to this cause
we owe in part the fact that in the wrinklings of the crust due to the
contraction of the interior the lands exhibit a prevailing tendency to
uprise, while the ocean floors sink down. In this way the continents
are maintained above the level of the sea despite the powerful forces
which are constantly wearing their substance away, while the seas
remain deep, although they are continually being burdened with
imported materials.

[Illustration: Fig. 8.--Diagram showing the effect of the position of
the fulcrum point in the movement of the land masses. In diagrams I
and II, the lines _a b_ represent the land before the movement, and
_a' b'_ its position after the movement; _s_, _s_, the position of