Wisconsin. Chief Geologist / Geology of Wisconsin. Survey of 1873-1879 ...
Volume II (1877)
Chapter V. The quaternary deposits, pp. 608-636 PDF (11.0 MB)
GEOLOGY OF CENTRAL WISCONSIN. CHAPTER V. THE QUATERNARY DEPOSITS. TTIE GLACIAL DRIFT.' The first and most striking fact that presents itself to the investi- gator of the drift phenomena of Wisconsin is the existence of an extensive driftless region, the remainder of the state at the same timte displaying an altogether extraordinary development of the drift materials. In the driftless region, which occupies 12,000 square miles of the southwestern part of Wisconsin, or nearly one fourth the entire area of the state, the drift is not merely insignificant, but absolutely wanting. Except in the valleys of the largest streams, like the Wisconsin and Mississippi, not a single erratic bowlder, nor even a rounded stone, is to be seen throughout the district; whilst the exception named is not really an exception, the timall gravel deposits that occur on these streams having evidently been brought by the rivers themselves, during their former greatly expanded condition, from those portions of their courses that lie within the drift-bearing regions. The outline of the driftless area is for the most part quite sharply defined, both by a more or less sudden cessation of the drift materials, and by a change in the topography as the line is crossed from one side to the other. This is more especially true of the east- ern boundary, close to which are often found heavy morainic heaps, with numerous bowlders of a large size, and oln the different sides of which the topographical effects of purely subaerial erosion with- out drift, and those of partial glacial erosion. with drift, are strongly contrasted. The northern b)oundary, oln the contrary, is largely in a level country, the drift naterials increasing quite gradually in quan- tity as it is left behind to the southward. ' It is not possible to give, in the space available, m ore than a brief summary of the large amount of material with regard to the glacial drift, that has been obtained during the survey of the Central Wisconsin district, -with the main conclusions reached. These, it is believed, when taken together with the results of the work of other meam- bers of the corps, will be found of considerable interest. 608
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