\ 
Major Lachlan on the Rise and Fall of the Lakes. 167 
of a lower mean temperature and diminished evaporation during 
the period of rise, and the reverse during the time of fall of the 
water-level. During 1838-39, the waters were higher than they 
had been before for at least two centuries. This is demonstrated 
by the large tracts of land that were inundated which were cov- 
ered with forest trees, many of them the growth of ages. These 
trees were destroyed by the overflow around Lakes Erie and Hu- - 
ron, and on the Ste. Marie river, between Point Detour and the 
Sault Ste. Marie. 
“We have no accounts of Lake Superior at that time; but 
there are facts that indicate a marked variation within a few years. 
In 1845 a rock in the middle of the entrance of Eagle Harbor, 
showed itself only in the trough of the waves; and the narrow 
outlet between the west end of Porter’s Island and the main land 
at Copper Harbor, was of such depth that loaded boats could 
enter without touching the rocks. In 1846, the rock at the 
mouth of Eagle Harbor was one-and-a half feet above water ; 
and boats could not get into Copper Harbor. In June, 1847, the 
tock above-mentioned was still more above water, and the outlet 
to Copper Harbor could be crossed by stepping on the projecting 
Points of the reef, without wetting the feet; an uring some 
depressions of the water by barometrical waves, it was laid almost 
entirely dry. From the 18th of June to the 6th of September 
there was a rise of full twelve inches. It has been observed on 
this lake that the water is lowest in spring and highest in autumn. 
is is readily explained by the fact that in winter most o the 
ordinary supplies of water from the drainage of the surrounding 
country are cut off, by being converted into ice and snow; while 
€vaporation from the, surface of the Lake by the dry northern 
Winds continues to carry away a very sensible quantity of water. 
During the Spring, on the contrary, the snow and ice melt, an 
the accumulated stores of winter flow into the Lake in greater 
quantity than to compensate for the evaporation and the drainage 
atthe outlet. . . During a century past the waters of Lake 
Uperior cannot have been more than four feet above the level of 
1847, for any considerable time, as is evident by the growth of 
tees of two feet in diameter at Porter’s Island, which would have 
died had the ground around them been inundated for any great 
ngth of time. . 
+0 descend once more to Lake Erie. Iam next indebted to 
Col. Whittlesey, Topographer to the Geological Survey of Ohio 
for eatowing, confined to the annual and daily fluctuations in 
* See Colonel Whittlesey’s Report for 1838-39. 
