The pre-Wisconsin or older terraces of the Driftless Area of Wisconsin are formed of much weathered and much eroded glacial outwash and nonglacial stream deposits, most of which lie on rock benches and some of which are nearly 200 feet above the present streams. These terraces, which are much older than the terraces of the Wisconsin glaciation, may be divided into at least two groups, whose formation was separated by a long period of erosion. The old stream deposits are of the same mode of origin as the younger, or Wisconsin, terrace deposits. The pre-Wisconsin terraces can not yet be correlated with particular glacial stages. These terraces are much like the old terraces of the upper Ohio basin.

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