The geological phenomena connected with all these lakes
have not, however, been investigated with sufficient accuracy and
detail, nor has there been any comparison of them extensive and
comprehensive enough to justify the adoption of any theory respecting
their origin. In an excursion to Lake Superior, some years since, I
satisfied myself that the position and outline of that particular lake
had their immediate cause in several distinct systems of dikes which
intersect its northern shore, and have probably cut up the whole tract
of rock over the space now filled by that wonderful sheet of fresh water
in such a way as to destroy its continuity, to produce depressions, and
gradually create the excavation which now forms the basin of the lake.
How far the same causes have been effectual in producing the other large
lakes I am unable to say, never having had the opportunity of studying
their formation with the same care.
The existence of the numerous smaller lakes running north and south in
the State of New York, as the Canandaigua, Seneca, Cayuga, etc., is more
easily accounted for. Slow and gradual as was the process by which
all that region was lifted above the ocean, it was, nevertheless,
accompanied by powerful dislocations of the stratified deposits, as we
shall see when we examine them with reference to the local phenomena
connected with them.
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