. 
; 
2 
On the Tides in the great North American Lakes. 217 
wig ie oe 
Mr. Schoolcraft has incidentally remarked, that it would appear 
natural for all the lakes to subside in a degree during the winter 
‘months. Evaporation and other wastes goon as during the summer 
months, though with diminished effects, while the ice and snow with- 
hold from the tributary streams all the moisture of the earth’s sur- 
face, and leave their channels almost dry. This opinion, so well 
founded in natural causes, is partly sustained by facts. It has been 
often observed that the ice, connected with the shore, is generally, 
before it breaks up or dissolves, found depressed below its first level. 
effect was not so sensible in the winters of 1828-9 and 
1829-30, as to be noticed at Detroit. | , 
From the foregoing remarks, the conclusion may be drawn, that 
there has been a periodical elevation of the upper lakes once in about 
fourteen years ; or, that its recurrence has been sufficiently precise, 
to authorize the popular belief of its regularity. But we are con- 
strained to suppose, although destitute of the light of all observations 
on the subject, that they must have been caused by unusually abun- 
dant rains and snows, and that this abundance has been in fortuitous 
coincidence with certain cycles of time; for, improbable as this may 
be, it is less so, than that nature should have departed from her or- 
dinary course. ' < 
. Since closing the foregoing remarks, I have been favored with the 
following letter from Gov. Cass, which expresses his opinion ‘fully on 
€ subject, and forms a valuable commentary on it. 
“ Derroit, March 24th, 1831. 
: Sir—In the conversation we had respecting the existence of tides 
the lakes of this region, I referred to a series of observations, 
made by myself at Green Bay, in August and September, 1828, 
With a view to determine this long disputed question. ‘This paper 
Tnow enclose to you, to dispose of as you think proper.* The place 
of observation was upon the Fox River, about three miles above its 
thouth, and two miles below the point, where the current ceases to 
be perceptible. A cask was securely placed near the bank, and a 
graduated rod fixed in it. |The cask was sufficiently open to show 
the rise and fall of the water, without being affected by the ripples on 
the surface, occasioned by the wind. It was my intention to record 
the state of the water at regular intervals, and this, as you will per- 
teive, Was generally done. But sometimes circumstances intervened 
O.Wit raw my own attention, or that of others from this duty, to 
ee. 3 
* See the Table, page 200. 
