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BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



height is a number of feet, the cusp is probably a two-swing cusp, 

 because the two levels are then best explained by different (but not 

 necessarily successive) swings of the meander belt. Examples of these 

 forms are often met with. 



Ideal Terrace Pattern : Middle Stage. If the sweeping and swing- 

 ing of the river continue until, as in Figure 11, a fifth return of the 

 meander belt to the western side of the valley is accomplished, a ter- 

 race pattern of some complication may result. Few and small remnants 

 of the higher terrace plains are to be expected at this stage, for they 

 have been repeatedly undercut and destroyed. Larger and more nu- 

 merous remnants of the lower plains may be still preserved, for they have 



Fig. 11. 



been less frequently attacked. A triangular portion of the third-swing 

 plain is shown in the middle of the figure ; on the right appears a still 

 larger piece of the fourth-swing plain, from which the river was with- 

 drawn by a short cut across the flood plain (not shown in the figure), 

 leaving an unfilled channel which now guides a small brook. The fifth 

 westward swing of the river has, during the down-valley sweep of a 

 single meander over the length of the diagram, undercut and destroyed 

 part of the fourth-swing plain on the right ; it has destroyed all of the 

 fourth-swing and part of the third-swing plain in the middle and all of 

 the earlier plains toward the left, where the meander undercuts the high 

 scarp and recent landslips have occurred. The greater the number of 

 swings, the smaller and rarer will be the remnants of the higher ter- 

 race plaius, unless some special control is present to preserve them. 

 A special interest attaches to the form and arrangement of the cusps 



