90 Davis — Terraces of the Westfield Biver, Mass. 



terraces only here and there, now and then ; and hence the 

 destruction of the lower southern terraces by the southward 

 shifting of the belt of river-swinging can only be accomplished 

 progressively. Thus viewed, it is no wonder that some of the 

 lower southern terraces still remain. This corollary to the 

 explanation above suggested receives much support when 

 examination is made of the relation between the defended 

 cusps of the terraces on the north and the concave reentrants 

 of the terraces on the south, to which we now proceed. 



13. Correlation of terraces on the two sides of the valley. — 

 It will be readily understood that, wherever a terrace scarp 

 curves forward from a concave reentrant to a defended cusp, 

 the river must have once flowed along the base of the scarp 

 and must have continued the line of the terrace curve past the 

 cusp toward the opposite side of the valley, there to recurve 

 toward the general valley axis. The farther forward the 

 defended cusp reaches toward the axis of the valley, the more 

 likely it is to direct the departing river strongly against the 

 terraces on the opposite side of the valley. Thus the curved 

 scarps, K^, K^^, K^^^, of the northern terraces, suggest that the 

 river has formerly flowed on past the defending ledges of 

 Perry's spur at these several levels and has thus entered the 

 reversed curves of the southern scarps, S^, S^^, S^^^ The levels 

 of the terraces concerned seem to correspond by pairs, but they 

 have not yet been accurately measured. Of the three northern 

 scarps, the one leading to K^ has the strongest curvature, for 

 the middle of its reentrant is cut farther back than the middle 

 of the others. When the river flowed at the base of this scarp, 

 its current must have departed from the defending ledge almost 

 transversely to the general eastward course of the valley. Con- 

 sequently the corresponding southern scarp, S', makes a strong 

 reentrant on the south" side of the valley. The second scarp, 

 K^', of the northern group was more gently curved ; the third 

 scarp, W, still more gently curved ; and the same relation is 

 seen in S'^ and S^^^ It is possible that even the higher southern 

 reentrant, S, is indirectly related to the ledges of the northern 

 valley-side about K ; the general curvature of the river being 

 determined by the ledges and a southward swing of the curving 

 river there causing the excavation of the reentrant, S. It is 

 proposed to make a careful measurement of all these terraces in 

 order to test their correspondences. 



Another example of this cross- valley relation is found far- 

 ther west. The curved scarp of the lowest northern terrace, 

 N', that sweeps out to the defending ledges at M, is the north- 

 ern member of a double curve whose southern member made 

 the strong concave sweep, P, already mentioned, under the 

 high southern terrace plain. The ledges at M stand unusually 



