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 produced. 



Fig. 24. 



The special features of terraces 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 irs 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 2G ; it lies somewhat below 

 the apex of a down-sweeping meander. Assuming that the meander 



