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bulletin: museum of comparative zoology. 



meander cuts below the plain of its predecessor. The curves and cusps 

 of Terrace B result from a vacillation of the meander during its 



Fig. 9. 



down-valley progress ; a rather sharp cusp being left between B 2 



and B 3, while the curves from B 3 to B 9 have arcs so small as to 



join in a nearly straight terrace front. 



It may be noted that the small curves 

 by which a nearly straight terrace front 

 is usually formed are as a rule to be ex- 

 pected only towards the side of a valley, 

 and less commonly on a terrace spur that 

 advances into the valley. For example, 

 in Figure 10 the little curves A, C, D, E, 

 record so many positions of the meander 

 apex, and will not now be destroyed until 

 a later meander under-cuts them. Scarps 

 of this kind may be called one-sweep scarps ; 

 and their cusps, one-sweep cusps. Several 

 similar cusps are shown in Figure 9. The 

 longer curve, E E', cut by the advancing 

 front of the meandering river, may be 

 abandoned if the river is diverted by a 

 Fig. 10. short-cut to a new course, and if so the 



advancing terrace spur will be smooth trimmed. 



