14 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
The compound movement of meanders sweeping in a swinging 
meander belt is called wandering. The whole breadth of the valley 
floor, which may be worn down by the stream, is known as the belt 
of wandering,— a belt which corresponds to our familiar flood plains. 
It is now recognized that the meanders sweep down the valley and 
therefore pass progressively any given point; and since at the same 
time the river is degrading, each successive meander must pass at a 
slightly lower level. The amount of difference in level is compara¬ 
tively little. In the much longer time necessary for the entire river 
to swing across its wandering belt, the river degrades more markedly, 
carving a deeper scarp. Ordinarily the scarp separating terraces is 
a measure of the amount of down-cutting the river has accomplished 
in swinging across the valley and back (profiles, plate 2). The terraces 
left after the river has swung several times across its valley will vary 
in width, and they stand as remnants of the flood plains. 
According to Davis (’02, p. 298), the behavior of a wandering river 
rests upon four postulates: “(1) The degrading stream continually 
maintains an essentially graded 1 condition. (2) The lateral swinging 
of the meandering channel is very much faster (a hundred fold, for 
example) than the degradation of the valley floor. (3) The breadth 
over which a free river (not constrained by ledges) tends to swing 
laterally is greater than the breadth of the meander belt (the belt 
included by tangents to the meandering channel). (4) An individual 
meander tends to enlarge its radius and to work its way down the 
valley until it may be abandoned at season of high water for a short¬ 
cut across a flood-plain lobe, or at any season (but usually at high 
water) for a cut-off through the narrowing neck of a lobe.” To these 
postulates may be added a fifth: any departure of the thread of the 
current from the delicate adjustment of its symmetrical curves, caused 
by change of volume, cut-off, short-cut, rock barrier, accidental natural 
obstruction, or artificial construction, deflects the curving thread of the 
current throwing it into a new series of meanders. 
Theory of River Terraces. 
In order better to appreciate the work which the West and Connecti¬ 
cut Rivers are accomplishing, it may be well at this point to review the 
1 It may be pertinent to state that a river is graded, if at high water it falls in a 
gentle unbroken slope to the sea. A graded river may at low water reveal rapids, for 
a river though practically graded, is slowly degrading. 
