FISHER: RIVER TERRACES. 
13 
Origin of river terraces in New England. — The stepping terraces 
of our valleys suggest a narrowing meander belt, a broad valley floor 
for the carving of the higher and older terraces, and a narrower valley 
floor upon which the rivers are to-day meandering (see profiles, plate 
2). Three theories offer an explanation of this shrinkage of the mean¬ 
der belt. The first theory assumes a diminution of stream volume dur¬ 
ing and after the uplift which caused the rivers to degrade. It is 
supposed that the greater volume of the rivers necessitated a greater 
arc of curvature and a broader space on which to swing. To-day the 
streams are weakened by the loss of much of their former volume, and 
therefore swing with shorter arc of curvature over a more limited area, 
and in consequence have not the power to undercut and remove the 
terraces of earlier date. 
The second theory postulates that the lower and lower terraces are 
the result of successive uplifts of the region. The river revived by 
each uplift cuts its channel beneath its former flood plain until grade 
is reached and the river swings laterally. Allow less and less, time to 
elapse between successive uplifts, and there would be a diminution 
in the amount of lateral swinging as the valley was worn deeper. 
The third theory (suggested by Miller, ’83) points to a slow regional 
uplift as the cause of valley erosion and then calls attention to the 
rock ledges discovered by a wandering river at successively lower and 
lower levels producing narrower and narrower interscarp terrace 
plains and the observed shrinkage of the meander belt. It is this 
third theory which is competent to account for the occurrence and 
pattern of our New England terraces. The importance of this theory 
has been recognized and fully demonstrated by Davis (’02; ’02a), 
Terminology of winding rivers .— It may be well to summarize the 
terms used in considering the processes of river terracing. A mean¬ 
der belt covers the area included between tangents drawn outside of the 
bends or meanders of a stream. This belt widens as the meanders 
push outward or wear away their banks. It may also collapse locally 
in the case of a cut-off or short-cut. As the river moves laterally, 
the process is known as swinging. The meanders may be said to 
sweep progressively down the valley. “Up-stream” and “down¬ 
stream” refer as usual to the motion of the current, whereas “up- 
valley” and “down-valley” indicate a more general direction than 
that of the circuitous channel of the stream. The terms “right” 
and “left” relate to the down-stream direction of the current. 
