HURONIAN AGE.


2    maxuam Acidity in the Ilaronian. We may, perhaps, be justified
in suggesting the broad generalization that the sediments increased
in silicious character until the Huronian era, when they reached their
maximum, beyond which they remained in equilibrium or declined.
Canadian Formrations. In Canada and adjacent regions of the
east, there exist extensive deposits of limestone, iron ores, and car-
bonaceous shales, which were formerly classed with the Laurentian,
but which Dr. Selwyn, the present director of the Canadian survey,
identifies with the Huronian. He refers to the Laurentian only
the great series of gneisses and allied highly crystalline rocks. It
will be observed that this view brings into striking harmony the
Canadian and Wisconsin series, and this concordance lends support
to Mr. Selwyn's views. For while mechanical sediments might
vary materially within the space of a few hundred miles, it is far
less likely that a profound change should be suffered by an immense
system of rocks, involving (besides a great variety of mechanical
sediments) limestones, carbonaceous deposits, and iron ores. We,
therefore, adopt with much confidence this classification.
l§rfe of the Eta. No identifiable fossils have yet been found in
the Huronian series of Wisconsin. Some obscure organic remains
are thought to have been found in the adjacent region of Michigan,'
and in the supposed equivalent in Canada, as before mentioned, the
Eozoon Canadense has been found. Some additional supposed organic
remains are reported from the same series. 2 But none of these seem
in themselves to be absolutely indisputable. Notwithstanding this
meagerness of direct evidence, the existence of great deposits of
limestone, carbonaceous material and iron ore, leaves little room for
rational doubt of the existence of life. Probably the limestones of
the age were derived, like those of subsequent times, from the cal-
careous remains of marine animals. The carbonaceous deposits
probably arose from plant accumulations. It seems most probable
also, as already indicated, that the iron ores were, in the main, con-
centrated through the agency of organic matter. Taken together
these present a strong case of " circumstantial evidence."
Pertiod of Hauronian Upheaval.
Succeeding the period of Huronian sedimentation, whether im-
mediately or somewhat delayed, there was an era of upheaval and
metamorphism, analogous to that which occurred at the close of the
Laurentian era. It produced analogous, but less extreme effects.
1 Geol. Surv. Mich., Vol. II, p. a.
'Geol. Surv. Wis., Vol. III, p. 561


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