Wood County reporter. [volume] (Grand Rapids [i.e. Wisconsin Rapids], Wis.) 1857-1923, 1888-07-26
THE GREAT LAKES.
Geological History of Their Formation and
Change in Their Level

HE GREAT LAKES.
Ueoiogieal History OF Their Formation and
Change in Their Level
The Forum for June contains an article
by Z. h. Gilbert on Changes of Level of
the Great Lakes. Promising that lakes
are destroyed by rivers, by the double
process of filling them up with sediment
and of deepening the channel of escaDe
and that, on the other hand, lakes are
formed chisfy by the upheaval of the
earth's surface and by its erosion by the
movements of glaciers, the author de
votes the greater part of his article to the
geologic history of the formation of
the great lakes. Their beds, with the
possible exception of Erie, we're secured
out Of the solid rock by the great glaciers
OF the ice age, but accumulation of de-
bris III many cases increase their depth
and influence the G.-ectiOn OF their cut
flow. The removal OF this debris in the
case of the Erie, for instance would 70
duce 1t greatly perhaps entirely drain it
and would make it flow into Ontario and
Hamilton. The increase of heat caused the
edge of the great glacier 10 retract from
the southern border at Fort Wayne, where
the water generated upon it flowed into
Ontario into two lakes. But as long IS
the ice remained in the st. Lawrence val
ley the waters found their escape into
the Mohawk at Rome. One of the
beaches formed by the action OF the
waves has its crest marked by the ridge
road from Lewiston to Sodus. At this
time Lake Erie was only one-third as long
as now, and its surface was only One-fifth
as great, Toledo, Cleveland, and the Bass
islands being far inland. When Lake
Ontario forced new outlet through the
st. Lawrence valley its lever was drawn
down five hundred feet aud its area re-
dUcsd 80 per cent, becoming 80 per cent.
smaller than ct present. The rising of
the depressed land to the northwest gave
the lakes their present dimensions, and
the oscillation then received a check. "a
further fitting of the land to the extent
of three inches in each mile would send
great river from Chicago to the Missis-
sipi, reverse the current in the Detroit,
stop Niagara falls, and rob the upper st.
Lawrence of seven-eights of its water.'
Whether, contrary to what appears to be
law against absolute stability, the osolll-
alton has entirely ceased or not, it is
now SO slow as to prevent the detection
of any movement, the present level of
the water having remained nearly con,
tant for many centuries.
Other changes are, however, In progress
from the actions of the rivers. The st.
Clair is feebly securing its channel and
building its delta; the Niagara is eating its
way back to Lake Erie; the st. Marie,
Detroit, and st. Lawrence are deepening
their channels. "All these processes ale
too slow to affect our hopes and fears con-
cerHing che immediate futare, and for
our posterity in the year 10000 we have
no soiicitude. The men Who shall watch
the draining of Lake Erie-or who,
perchance, shall find IL worth their while
to prevent twill as far surpass us in
powers and resources as we surpass the
men who watched the lakes creation.
For all practical purposes our inland seas
are permanent and their basins stable.
The only notifications that affect our
economy are those wrought by the waves
upon their coasts" The changes in the
water levels that are noticed are due to
the variations in the rainfall upon the
lakes themselves and upon the land drain
ed by the streams that pour into them.
The amount of rainfall varies from year
to year and from enc season to another
IN the same year, and the level of the
water ocillates around an average position
that remains fixed. Thus during the
period from 1850 TO 1887, the mean an
nual range of Lake Erie was 1.6 feet, and
the extreme range for the same period
3.5 feet. In 1888 Lake Erie rose Is inches
above its ordinary high stage, and in 1873
it fell 80 feet below its usual plano. "The
present low water is the sequel Of last
sumn4fr's drought" the lake region hav-
ing received only about % inches of rain
fall instead of It's usual SO inches. This
should cause fall of TIE lakes of about
Ia inches, half from direct loss and half
from the loss of the streams that empty
into them. But tbs average fall of all the
akes was about inches, owing probably
TO the GOODNESS of the autumn, which re-
tarded evaporation. In Lake Superior
The fall was 3 inches below the average
ow stage, the lowest point reached in
seventeen years except Oh two occasions.
Ia Erie IL was two inches below the aver
age.
These variations relate to the entire
surfaces of the lake. A part of one may
30 depressed and another part raised by
gale, especially in the case of Lake Erie,
IN account of its shallowness. gale
las been known to raise the level of one
u lto Suu5 StFOA u SlSlb l66b anu W ne
'ress the other to an equal amount. Diff
erences in atmospheric pressure also eff
ec5 different parts of the same lake. The
apid change of air pressures, as in the
ase of tornadoes, sometimes causes
hythmic undulations as high as the lsrg-
S. created by the wind. There are
lso tides which are as regular as on the
oean, but the highest spring tide rises
My about three inches, while the aver
&c height is probably not more than an
lch.