. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. DAVIS: RIVER TERRACES IN NEW ENGLAND. 313 made before the swinging stream has entirely consumed the terrace of the previous swing. Every return of the swinging river against a sloping reef of rocks will thus be recorded by a little strip of terrace behind the defending ledges, and a flight of stepping terraces will necessarily be produced wherever a large group of ledges slopes under the valley drift into the belt of river action. The length of the ledge exposed at the back of each terrace may be but a few fe
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. DAVIS: RIVER TERRACES IN NEW ENGLAND. 313 made before the swinging stream has entirely consumed the terrace of the previous swing. Every return of the swinging river against a sloping reef of rocks will thus be recorded by a little strip of terrace behind the defending ledges, and a flight of stepping terraces will necessarily be produced wherever a large group of ledges slopes under the valley drift into the belt of river action. The length of the ledge exposed at the back of each terrace may be but a few feet, but its effect will be prolonged by a trailing terrace, as it may be called, stretching hundreds or thousands of feet along the valley side. It is in this way that the best flights of stepping terraces are Fig. 24. The special features of teiraces associated with defending ledges are next to be examined. Slipping Meanders and Blunt Cusps. It has not yet been possible to discover by observation how a down-sweeping meander will make its passage past a ledge ; but it may be inferred from the forms of terraces found in various valleys that a stream has two methods of procedure in such an exigency. The first is considered in this section, and is illus- trated in Figures 25 to 28 ; the second is taken up in the next section, with Figures 29 to 31. Let it be supposed that the river in Figure 25 is now making its fourth swing against the western side of its valley, and that a buried ledge lies a few hundred feet back of the group of free cusps in the middle of the diagram. The ledge is discovered in Figure 26 ; it lies somewhat below the apex of a down-sweeping meander. Assuming that the meander. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Harvard University. Museum of Comparative Zoology. Cambrid
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