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Histories:  Trempealeau Co. Historical Accounts:

"History of Trempealeau County Wisconsin, 1917":

Chapter 2

Recapitulation

(By George H. Squier)

 -As transcribed from pages 24 - 25

In reviewing briefly the facts of the preparation of Trempealeau County for the occupancy of man, a summary of the foregoing facts may prove of interest. At the end of the Pre-Cambrian period, Trempealeau County presented a sloping surface of bare rock, comparatively level, but containing some hills of moderate elevation. In the Cambrian period the region was depressed and covered with a shallpw sea. During this and succeeding periods various layers of sandstone (pulverized rock) and limestone (pulverized shells) were deposited in the bed of this shallow sea. Just which of these layers were laid down in Trempealeau County is somewhat uncertain. The Pottsdam sandstone and the Lower Magnesian limestone stoll remains, the latter being seen in the tops of the Mississippi bluffs. The region remained submerged during the Ordovician, Silurian, Devonian, Mississippian and most of the Pennsylvanian period. But toward the close of the Pennsylvanian, or in the Permian period, the region was elevated above the sea level. Streams began to cut valleys. When they had cut as deep as they could they began to widen these valleys. This process continued during the Permian, Triassic, Jurassic and Cretaceous periods until the region was again a great sloping level plain. This plain was surfaced with the Lower Magnesian limestone and coincided with the present tops of the Mississippi bluffs. But it rose rapidly in elevation to the northward so that the present hills in the northern part of the country are three or four hundred feet below what was then the surface of the plain. In the Tertiary period streams began cutting through this plain. A vast amount of material was removed and the present valleys were formed. At the opening of the Pleistocene Period the rock foundation of Trempealeau County lay practically in its present form. The valleys, however, were much narrower and deeper and the sides much steeper. Except for thin deposits of sandy soil, all the county was a region of bare and jagged rocks. Then came the Pleistocene Period with its glacial peripds, when glaciers formed and were melted again several times. A larger part of Trempealeau County is in what is called the Driftless Area, and was probably never covered with a glacier. But it was to the glaciers that we owe the present condition of the county. During the time of the glaciers the county received in the Mississippi, Black and, to some extent, the Trempealeau Valley, sandy pebbles carried by the streams flowing away from the glaciers, and during the several times that the county was submerged during this era, the bare valleys and foothills, lying in the bed of the muddy lakes, formed by the melting glaciers, received the deposits which now constitute the foundation of our soil. At times during the Glacial Periods the Mississippi bed was higher than at present and at times lower. The original bed of the Mississippi was probably over the Trempealeau Prairie, and the Trempealeau Bluffs are probably really an extension of the Minnesota Bluffs, the belief being that in this region the Mississippi is now flowing in what was the bed of a nearly parallel tributary. In the rich deposits left by the glacial lakes vegetation began to grow, and the decomposing vegetation mingling with the deposits formed the soil as it was found by the early settlers.




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