322 bulletin: museum of comparative zoology. 



cases, if at all ; but the terraces of Chicopee river above Beecham Falls, 

 a few miles northeast of Springfield, Mass., give some support to this 

 possibilitv. Further observation is needed in this direction. 



When two barriers occur near together, leaving a free space of half a 

 mile or so between them, the river is fixed at two nodes, but may 

 vibrate between them. A remarkable case of this kind is found in the 

 valley of Saxtons river at Bellows Falls, Vermont, as described on 

 page 337. 



Relation of Terrace Patterns on the Two Sides of a Valley. It 

 has been already pointed out as a matter generally accepted by many 

 observers, that the terraces on the two sides of a valley need not neces- 

 sarily agree in number or in height. The relations of terrace patterns as 

 seen in plan on the two sides of a valley have been less considered. It 

 is desired here to indicate certain relations that seem to obtain in special 

 cases. 



When a group of defended cusps occurs in a valley of moderate 

 breadth, the stream must have been repeatedly deflected across the 

 valley by the defending ledges, so as often to impinge upon the opposite 

 side of the valley in about the same place. Hence re-entrants of more 

 than usual size may there be worn out, next up-valley from which a 

 group of free cusps may thus come to stand about opposite the defended 

 cusps. If the meander next above the ledge is somewhat compressed, 

 the stream may strike more squarely across the valley and under-cut the 

 down-valley side of a terrace with somewhat greater vigor than usual. 

 The valley of the Westfield river, a mile or so up-stream from West- 

 field, Mass., offers some remarkable examples of this kind (page 333). 



When a side stream enters the valley of a degrading main stream, it 

 tends to push the main stream away, and thus causes it to wear out 

 re-entrants opposite to the entrance of the side stream. Reacting from 

 such re-entrants, the main stream will strike across the valley and scour 

 out another group of re-entrants below T the mouth of the side stream. 

 When this transverse deflection of the main stream is confirmed by the 

 occurrence of a guiding ledge, the re-entrants will be all the more per- 

 sistently and repeatedly carved out. The Connecticut seems to show 

 an example of double control by the Westfield and by ledges in the 

 southern part of Springfield, Mass. (page 344) ; and the Westfield itself, 

 two miles east of Westfield village, offers a similar example of double 

 control (page 330). 



Ratio of Sweeping, Swinging, and Degrading. The foregoing analyses 

 of the process by which a graded and wandering river may degrade and 



