p. 100

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110

Geology—Primitive [District?]

Hornbleude rock in is found at many of the Rapids on the
upper Mississippi; and it constitutes that rough, high
broken momentary extending into Lake Superior between
the days of [Fond=du=Lac?] and Chegoimegan, called the
detour. A large proportion of the boulders contain
more or less hornbleude in their composition. Some
of the rocky islands of the Lake of the Woods and of Rainy Lake
are composed of Sienite, which also occasions the falls
at the outlet of the latter, where the water falls into the
river over a ledge twenty five feet high. [Argielite?] is
found at the "Portage aux Coteau" on the St Louis river; the
sharp edge of its vertical layers occasion much inconvenience
in [illegible] the portage. Serpentine is found in small
masses on Lake Superior containing grain of native
copper. It is also said to be found in connection with the
celebrated copper rock from the Ontonagon view, now
in the [cabinet?] of the National Institution at Washington.
To discover the locality of this rock in nature beds
then, becomes an important [desideration?].

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