DAVIS: RIVER TERRACES IN NEW ENGLAND. 305 



A terrace whose scarp has been almost evenly trimmed by the small 

 vacillations of a down-sweeping meander will face the axis of the valley. 

 A terrace whose scarp has been under-cut by the forward half of a down- 

 sweeping meander will face obliquely up the valley, as in the foreground 

 of Figure 10. Inasmuch as the normal progress of meander-sweeping is 

 down the valley, it would seem, at first thought, that no terrace scarps 

 could be carved so as to face in that direction ; but on second thought it 

 will be seen that the lateral growth of a meander may cause part of the 

 curve to grow up-valley faster than the meander is carried in the other 

 direction by the normal down-valley sweeping of the meander system ; 

 and in this case a terrace scarp facing obliquely down-valley will be 

 carved. An example of this kind is shown near the foreground of Figure 

 11. It is manifest that the development of terraces facing down- valley 

 will be favored wherever the down-valley sweeping of a group of mean- 

 ders is for any reason checked while the enlargement of their curves is 

 continued. 



There can be little doubt that the height of terraces produced by the 

 action of successive meanders would be very small, hardly measuring as 

 many inches or quarter inches as actual terraces measure in feet. Let 

 it therefore be now supposed that after a series of one-sweep scarps has 

 been carved, the river swings away from the western side of its valley 

 and for a time occupies itself in carving scarps on the eastern side. 

 Many meanders will have swept down the valley during the eastward 

 swing of the meander belt, each meander leaving its faint scar on the 

 valley floor. When the river swings westward again, it will be working 

 at a lower level than before, and as it then once more undercuts the 

 high plain, a distinct terrace with a scarp of ten or twenty feet will be 

 formed. Terraces of distinctly different levels may therefore usually 

 be taken to represent different swings of the meander belt ; terraces 

 that represent only the sweeps of successive meanders while the belt 

 remains almost stationary must be so faint as to be hardly noticeable. 



A cusp which results from the slightly vacillating forward sweep of a 

 single meander, as B 6, B 7, etc., Figure 9, has already been called a 

 one-sweep cusp. The terrace plain extending forward from the base 

 of such a cusp will be a smoothly continuous surface on both sides of 

 the apex. When the two parts of a terrace plain on either side of a 

 cusp differ in height by a foot or two, they are probably the product of 

 different (but not necessarily successive) meauders ; and such a cusp 

 may be called a two-sweep cusp, because the two levels probably repre- 

 sent different sweeps in the meander belt. When the difference in 



