GENERAL GEOLOGY.


It is a necessary inference, therefore, that this formation originally
covered a very large area in the southern portion of the State.
Similar observations upon other formations lead to similar views
concerning their former greater extension.
It is our judgment, from a somewhat careful consideration of the
data bearing upon the subject, that the Potsdam sandstone, and
Lower Magnesian and Trenton limestones, originally wrapped en-
tirely around the Archvean core of the State, but that they never
buried the island thus formed, which always stood as a source of
material and a sentinel of the growing State, whose motto, "For-
ward," impressed thus early upon it by Nature's seal, forbade it,
having once risen from the ocean, ever again to subside completely
beneath it. The Niagara group may once have covered one-third
of the area of the State, embracing the older nucleus between arms
extending high up on either side, but probably not surrounding it.
The Devonian beds probably only extended a short distance inland
from the Michigan shore, while on the western side, their probable
limit, as already suggested, was the present position of the Mis-
sissippi river.


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