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