

302 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



the stage of development may be stated in terms of the flood-plain 

 pattern. 



The four postulates above announced concerning river action may 

 therefore be taken as well supported. 



A natural limit is set to the dimensions of a growing meander curve 

 on a flood plain by the formation of short-cuts across flood-plain lobes at 

 time of high water, or of cut-offs when the narrowing neck of a lobe is 

 finally worn through, a roundabout course being in both cases abandoned 

 for a more direct one. It may therefore be expected that the abandoned 

 channels, such as are preserved in ox-bow lakes on existing flood plains, 

 and in swampy half-filled channels at the back border of many terraces, 

 will on the average show a larger radius of curvature than the curves 

 of the existing river; and the maps of the Mississippi give some support 

 to this expectation. Emerson has pointed out (735) the tendency of our 

 New England rivers and streams to form loops or ox-bows on the right 

 of their general course, from which they return to a nearly direct course 

 by short-cuts or cuts-offs, only to begin again the work of right-handed 

 loop-cutting. He states that the Connecticut near Northampton, Mass., 

 has seven deserted loops on the right (west) and none on the left ; some 

 of its tributaries have sharp bends and ox-bows thirty times as numerous 

 on the right as on the left of their course. It is naturally suggested 

 that this asymmetry is the result of the deflective force arising from the 

 earth's rotation. 



Terminology of Wandering Rivers. The terms already introduced 

 regarding rivers that wander about their flood plains may now be sum- 

 marized and somewhat extended. The space enclosed between tangents 

 drawn outside of the curves or meanders of the stream is the 

 meander belt. This belt will widen while the meanders are normally 

 wearing their outer bank ; but on the occurrence of a short-cut across a 

 flood-plain lobe or of a cut-off through the narrowing neck of a lobe, the 

 belt will locally collapse. Here the river course becomes relatively 

 direct for a time, only to develop serpentines again as new meanders are 

 established. The progressive movement of the meanders down the 

 valley will be called sweeping. Up-stream and down-stream will be 

 used in their ordinary sense, but up-valley and down-valley will be 

 substituted when it is desired to indicate a more general direction than 

 that of the circuitous channel. 



The lateral movement of the meander belt from one side of the valley 

 floor to the other will be referred to as swinging. It is not always 

 possible to distinguish between the true lateral swinging of the meander 



