University of Wisconsin Digital Collections
Link to University of Wisconsin Digital Collections
Link to University of Wisconsin Digital Collections
The State of Wisconsin Collection

Page View

The history of Columbia County, Wisconsin, containing an account of its settlement, growth, development and resources; an extensive and minute sketch of its cities, towns and villages--their improvements, industries, manufactories, churches, schools and societies; its war record, biographical sketches, portraits of prominent men and early settlers; the whole preceded by a history of Wisconsin, statistics of the state, and an abstract of its laws and constitution and of the constitution of the United States
(1880)

Chamberlin, T. C.
Topography and geology,   pp. [110]-120 PDF (5.3 MB)


Page 115


TOPOGRAPHY AND GEOLOGY.
molten state, as has very generally been supposed, but was deposited by chemical
means after
the beds were formed and after a portion of the chemical change of the minerals
above mentioned
had been accomplished. The same is true of the silver. The copper occurs
in all the different
forms of rock-the melaphyrs, amygdaloids, sandstones, shales and conglomerates,
but most
abundantly in the amygdaloids and certain conglomerates.
     Thýis series extends across the northern portion of the state,
occupying portions of Ashland,
 Bayfield, Douglas, Burnett and Polk counties. When the Huronian rocks were
elevated, they
 carried these up with them, and they partook of the folding in some measure.
The copper-
 bearing range of Keweenaw Point, Michigan, extends southwestward through
Ashland, Burnett
 and Polk counties, and throughout this whole extent the beds dip north-northwesterly
toward
 Lake Superior, at a high angle; but in Douglas and Bayfield counties there
is a parallel range
 in which the beds incline in the opposite direction, and undoubtedly form
the opposite side of a
 trough formed by a downward flexure of the strata.
                      PALEOZOIC          TIME-SILURIAN              AGE.
                                    POTSDAM SANDSTONE.
     After the great Archaean u4pheaval, there followed a long period, concerning
wnich very little
is known-a "lost interval" in geological history. It is only certain
that immense erosion of
the Archaean strata took place, and that in time the sea advanced upon the
island, eroding its
strata and redepositing the wash and wear beneath its surface. The more resisting
beds with-
stood this advance, and formed reefs and rocky islands off the ancient shore,
about whose bases
the sands and sediments accumulated, as they did over the bottom of the surrounding
ocean.
The breakers, dashing against the rocky cliffs, threw down masses of rock,
which imbedded them-
selves in the sands, or were rolled and rounded on the beach, and at length
were buried, in
either case, to tell their own history, when they should be again disclosed
by the ceaseless gnaw-
ings of the very elements that had buried them. In addition to the accumulations
of wash and
wear that have previously been the main agents of rock-formations, abundant
life now swarms in
the ocean, and the sands become the great cemetery of its dead. Though the
contribution of each
little being was small, the myriad millions that the waters brought forth,
yielded by their remains,
a large contribution to the accumulating sediments. Among plants, there were
sea-weeds, and
among animals, protozoans, radiates, mollusks and articulates, all the sub-kingdoms
except the
vertebrates. Among these, the most remarkable, both in nature and ndrmber,
were the trilobites,
who have left their casts in countless multitudes in certain localities.
The result of the action
of these several agencies was the formation of extensive beds of sandstone,
with interstratified
layers of limestone and shale. These surrounded the Archaean nucleus on all
sides, and reposed
'on its flanks. On the Lake Superior margin, the sea acted mainly upon the
copper and iron-
bearing series, which are highly ferruginous, and the result wa; the red
Lake Superior sandstone.
On the'opposite side of the island, the wave-action was mainly upon quartzites,
porphyries and
granites, and resulted in light-colored sandstones. The former is confined
to the immediate
vicinity of Lake Superior; the latter occupies a broad, irregular belt bordering
the Archaean
area on the south, and, being widest in the central part of the state, is
often likened to a rude
crescent. The form and position of the area will be best apprehended by referring
to the
accompanying map. It will be understood from the foregoing description, that
the strata of this
formation lie in a nearly horizontal position, and repose unconformably upon
the worn surface
of the crystalline rocks. The close of this period was not marked by any
great upheaval; there
115


Go up to Top of Page