Although the retreat of the fall is slow,
it will in a very brief time, in the geo
logical scn=eof that word, lead to certain
momentous consequences. When the
hard layer of Niagara limestone passes
below the bed of the river, the stream will
then ent upon rooks of another constitu
tion, making for a time certain small
fails at a higher geological level; but in
the course of ages, much less long than
those which have elapsed since the birth
of this waterfall, the gorge of the river
will extend np into the basin of Lake
Erie, draining away a considerable por
tion of that fresh water sea.
We shall then, if the continent retains
its present height above the level of the
sea, have another system of cataracts in
the passage between Lake Erie and Lake
Huron, which will also in time he worn
away. Other cataracts wiil then form at
the exit of Lake Michigan; and thus the
lower lakes of our great American sys
ttm would be diminished in area, or per
haps even disappear. At a yet later
stage, we may iook for diminution in the
cize of Lake Superior, though that basin,
owing to the strong wall which separates
it from the lower lakes, is destined to en
dure long after the last named basins
have been diminished or entirely drained
away.
Proof Better Than Aiscrtion.
