. The environment of Camp Grant. se cases, the new drainage followed the old valleys where they werenot filled, and departed from them where they were filled. The valleys ofthe Rock and Kishwaukee rivers are examples of this type. ROCK RIVER VALLEY The history of Rock River valley in this region is both complicatedand interesting, and illustrates certain types of changes in drainage whichglaciation brings about. The history falls into four chapters. HISTORY OF THE LAND 45 1. The last ice-sheet which is known to have covered this regionis known as the Illinoian ice sheet. Before its advent, and
. The environment of Camp Grant. se cases, the new drainage followed the old valleys where they werenot filled, and departed from them where they were filled. The valleys ofthe Rock and Kishwaukee rivers are examples of this type. ROCK RIVER VALLEY The history of Rock River valley in this region is both complicatedand interesting, and illustrates certain types of changes in drainage whichglaciation brings about. The history falls into four chapters. HISTORY OF THE LAND 45 1. The last ice-sheet which is known to have covered this regionis known as the Illinoian ice sheet. Before its advent, and perhaps beforethe coming of any of its predecessors, there was a deep valley along thecourse of the present stream from the Wisconsin line down to a pointsomewhat south of the site of Camp Grant. Its bottom was more than250 feet below the channel of the present river. Below Camp Grant, ormore exactly, below the Kishwaukee, the continuation of this old valleywas to the south-southeast, instead of south westward as now (fig. 23).. PRINCETON L# Fig. 23.—The old course of Rock River, before the Illinoian glacial course of the river and its tributaries from the west is taken from Levereittamap in U. S. Geological Survey Monograph XXXVIII. 46 THE ENVIRONMENT OF CAMP GRANT North of the Kishwaukee thick deposits of drift were made in thevalley by the Illinoian ice-sheet, or its predecessors, or both; but thesedeposits nowhere filled the valley completely. At Rockford, where themap shows the valley to be narrow, a thick body of drift had been left inthe valley, almost choking it. The drift filling at this point seems to havebeen pushed in from the east, and crowded the river over to the west sideof its former valley, where the drift was shallow. Later when the channelwas lowered by erosion, the stream uncovered, for a short distance, thelimestone beneath the drift. This rock bed of the stream became the siteof a ford, and from this ford on rock came the name Rockford
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Keywords: ., bookcentury1900, bookdecade1910, bookidenviro, booksubjectgeology
