FISHER: RIVER TERRACES'. 
23 
sively added to the growing, undulating plain. The growth of such 
plains is more rapid immediately following the change in the deflec¬ 
tion of the thread of the current, and slowly decreases as the river 
approaches the series of normal curves. Since the rivers, though 
Fig. G.— Partition process of lateral movement; later stage of Fig.D, showing 
three islands which have successively parted the river. At times of suc¬ 
cessive erosion the deposition has been withdrawn from the former bank, 
causing the growth of the sand bars. 
graded, are constantly degrading, the deserted channels and the 
islands are successively lower and lower, and the flood plains though 
undulating, slope slightly toward the river. 
Such sand bars may be formed in any meandering river whether 
degrading, graded, or aggrading. By degrading, the more active 
streams drain the water from the growing partition plain, and by the 
continued deepening of the main channel the successive sand bars 
are exposed. They are narrow and show rather strong parallelism 
with the old and new river banks. The sand bars of the less active, 
more mature rivers accumulate slowly and form much more perma¬ 
nent islands. They are large in extent, often forest-covered and 
