Becker, George C. / Fishes of Wisconsin
Wisconsin waters, pp. 3-17 PDF (5.6 MB)
4 Wisconsin Waters Main Algonquin stage (slightly modified from J. L. Hough Geology of the Great Lakes, p. 294. University of Illinois Press, Urbana. © 1958 by the Board of Trustees of the University of Illinois) by glaciated regions: "It preserves a large sample of what the rest of Wisconsin, as well as northern and eastern United States, were like before the Glacial Pe- riod. Within the belts covered by the gigantic continental ice sheets of north- eastern North America and northwestern Europe there is no similar region of substantial size which was left bare of glacial ice" (Martin 1932:82). Black (1959) suggested that early ice of the Wisconsin glaciation may have extended farther into the driftless area than is shown on most published maps. The most sharply contrasting ecological conditions over wide areas of the state are between the driftless area and the area once covered by the glacier and glacial drift. Greene (1935:223-224) noted: Compared with the drift-covered area, the Driftless Area is rugged. Its central portion is floored principally by the Potsdam sandstone formation. In the northeast and extending in tongues down the valleys of the Black and Wisconsin rivers, the Archean granitic rock appears, while in the west and southwest the sandstone, overlain by a layer of limestone, is exposed only in the stream valleys .... The erosional system in the Drift- less Area has been at work over a relatively long period of time and streams have carved for themselves a mature, efficient drainage system. Swampy conditions are localized in the lower relatively flat river valleys, and the only natural lakes are Pepin and St. Croix, formed in the courses of the Mississippi and St. Croix rivers respectively by delta dams. The gradients of the streams in the driftless area are regular, with no natural swamps and no lake reservoirs. Such streams are subject to extreme fluctuation following wet and dry periods, and communities situated in their floodplains are subject to periodic flooding. In the glaciated regions, streams are controlled by slopes which are not gen- erally conducive to efficient runoff. In these regions, lakes, ponds, and marshes are the usual features. The phrase "imperfectly drained" is commonly used in )GRAPHIC LABORATORY, UNIVERSITY OF WI!
Copyright 1983. The entirety of this book is available for viewing by the public as an Open Access text through the cooperative efforts of George Becker, the University of Wisconsin Press, and the UWDCC. This Work is copyrighted to the Board of Regents of the University of Wisconsin System. Any use of this material falling outside the purview of "Fair Use" requires the permission of the University of Wisconsin Press.