Physical features of the Des Plaines Valley . III. IV Fig. 21. Diagrams showing the development of a straight waUed, flat flooredvalley, by the trimming away of spurs as the bends of the stream migrate down-valley. The river is flowing in the direction of the arrow. Four stages areshown. In I al, bl, ci, are three bends, which lie between three alternatingspurs, X, y, z. The valley bottom is narrow—no wider than the stream. In II thetendency of the stream to cut on the down-valley side of each bend has shiftedal, h\, and ci to the positions ai, hi, ci, leaving stretches of straight valley wall
Physical features of the Des Plaines Valley . III. IV Fig. 21. Diagrams showing the development of a straight waUed, flat flooredvalley, by the trimming away of spurs as the bends of the stream migrate down-valley. The river is flowing in the direction of the arrow. Four stages areshown. In I al, bl, ci, are three bends, which lie between three alternatingspurs, X, y, z. The valley bottom is narrow—no wider than the stream. In II thetendency of the stream to cut on the down-valley side of each bend has shiftedal, h\, and ci to the positions ai, hi, ci, leaving stretches of straight valley walls,ol-a2, bi-62, cl-c2. Across the river at each bend a portion of the up-valley sideof each spur, x, y, z, has been trimmed away, sharpening these spurs. A flat floor,of variable width (un-shaded) has thus been produced. In III the process has con-tinued. The bends have migrated down-valley to a3, 63, c3. The stretches ofstraight valley wall have been lengthened, ai-o3, bi-&3, cl-c3. The spurs x, y. z,have been half consumed by the trimming
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Keywords: ., bo, bookcentury1900, bookdecade1900, bookidphysicalfeatures00gold
