The Saint Paul globe. (St. Paul, Minn.) 1896-1905, 1899-06-11
BY GROVE KARL GILBERT,
Of the Geological Survs

/ CFrom Recent Earth Movement in the
Great Lakes Region" embodied in the
| eighteenth annual, report of the United
| States geologica4 $urvey0
| The ground at Milwaukee, compared
! with the ground at Port Austin, has sub
| sided Obs foot in the twenty years from
| 1876 to 1896. It isl the afgebraic sum of
| six measurements of which three
| dwellings, by water surface and three by
| the engineers level The probable
| rors of the water slevel measurement are
| 0019, 0.013 and g00Q2. The probable error
| of the Port Austin dwellings, in 1896, as
| Indicated by the discordance of two in
[ dependent results, lis COOS. If the proba-
BILE error of each. Of the other measure
ments was 0010, the probable error of
| the result is less than .03 foot.
In the discussion of the data used in
+ comparing the. several pairs of stations
it has been found that, taken at their
face value, they Indicate fitting in the
hypothetical direction, but it has also
/ been found impossible to resolve all
| doubts as tor the stability of the gauges
and benches and. the accuracy of the
measurements.
BY reason of these doubts the result
/ from ne single pair of stations is conclu-
I sive, but when assembled they exhibit a
7 harmony which argues strongly for their
| validity. Asitabulated, there are four
results, but these are not all independ-
| ent since observations and measure
| ments att Milwaukee aroused twice.
| THE RATE OF THE CHANGE I
/ There are however, three results whoH-
| 1y independent and a fourth partly indie
+ pendent, nameays the determination OF
change between Port Co1porne and G4eNe-
land for 8he shorter PERIOD lS72-1S95. Sos
/ Not oniNsdQ all these results Indicate a
change 1of the same sort,zbut they agrees
fairly well as to- quantity The eemputed.
| change for 100 miles in a century rangeS
| only from O37 to 046 foot.
The ldeduced mean rate of change-042
foot to the 100 miles in a century-de-s
ponds on assumptions which are eonven-s
lent rather than probable. These are:
% That the whole region moves togetf-
| er as a unit, being tilted without inter-
nal Wrapping, and % in the direction Of
its present fitting is identical with the
direction. of the total change since the
| epoch of the Nipissing outlet of the up
per lakes.
Assuming that the general result of
this, investigation is substantially correct
that the whole lake region is being
lifted on eoneNside or depressed on the
| other, so that itssplane is bodily canted
| toward the south-southwest, and that
the rate of change is such that the two
ends of a line 100 miles long and lying in
| a south-southwest direction are relatively
displaced four-tenths of foot in 100
years-certainssg general consequences may
be stated S.-sf
WATER ENERYWHERE RISING.
The waters Of the lake are gradually
rising on the southern and western
shores falling the northern and
eastern shoresl or both. This change is
not directly obvious because masked
by temporary changes due to inequalities
of rainfall and evaporation and various
other causes, but it affects the mean
height of the lake surface. In Lake On
| tarfo the waterStf is advancing all
shores. At Hamilton and Port Dali
housie it amounts to six inches In
century .;t
The water also advances on all shores
of Lake Erie, most rapidly at Toledo
and Sandusky where the change is eight
or nine inches century. All about lake
Huron the water is falling, most rapidly
at the north and northeast. where the
distance from the Port Huron isobase
is greatest; at Maekinac the rate is six
inches, and at the mouth of French river
ten inches a century.
On Lake Superior the isobaSe of the |
outlet cuts the shore at the fnterna=
t:onal boundary; the water is advancing
on the American shore and sinking on
the Canadian. At Duluth the advance is
six inches and atfHeron bay the recess
sion is five inches a century, The shores |
OF Lake Michigan ssare divided by the [
Port Huron isobase.
CANADIAN SHORE RISING.
North of .Oeento and Manstee the T
water is falling; south of those places it
is rising the rate at Milwaukee being five
or six inches a century and at Chica-
go nine or ten ;nche Eventually, I'M
less dam is erected to prevent. Lake
Michigan will again overflow to the Illi-
nois river it's discharge occupying the
channel loxyt ha outlet of q n1aiStO- |
Gene glacial lake.
The summit in that channel is now
eight feet above the mean level of the
lake. and the tinle9before it will be over
topped (under the stated assumption as T
to rate of tiltingS may be computed. Evil
IDENTIFY the first wafer to overflow will be
that of some high stage Of the lake, and
che discharge may as first be interTnit-
tent.
IN $500 YEARS No NIAGARA.
Such high water discharges will occur
in 500 or 600 years For the mean lake
stage such discharge will begin in about
1.000 years, andn after 1,500 years there
will be no interruption. In about 1000
years the Illinois, river and the Niagara
will carry equal portions of the surplus
water of the great lakes.
In $500 years the discharge of the Mag
ara will be fnteFnittent, failing at low
stages of the lake, and in $500 years |
there will be no Niagara. The basin of /
Lake Erie will then he tributary to Lake
Huron, the current being reversed In the |
Detroit and st. Clair channels.
The most numerous economic bearings |
OF this geographic change pertain to en-
gineering works. especially for the pres |
ervatfon of harbors and regulation Of |
water levels. But the notifications thus |
produced are so slow as compared to tho |
growing demands of commerce for depth |
Of water that. they may have small Inn |
pertance.
1t Is a matter OF greater moment that
citiaa and toWna built on loWlands about