22 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
left-hand meanders to a winding but much straighter course and 
each deflection has been so rapid as to leave a series of four distinct 
islands of less and less curvature from the former meanders to the 
present almost straight course (as illustrated by the photograph, pi. 
11, fig. 1). These resultant, undulating plains will be described under 
the development of partition plains. Other series of equally good 
sand-bar islands and one-time channels appear along the brook. 
These deflections have resulted from a large quantity of fallen tree 
trunks and brush, that initiated a left-hand deflection about a hundred 
feet up-stream from the road. At flood season short-cuts have been 
carved as a result of the new adjustment. At the lower end of the 
photographed meander, special sand-bar forms were constructed 
resulting from the discovery of a barrier of clay made firm by the 
roots of trees. This barrier chanced to be below the apex of a left- 
hand meander. The meander became more and more compressed 
causing the brook to bend up-stream to encircle the barrier, and that 
deflection enforced a withdrawal from the compressed bend and the 
formation of sand bar after sand bar until the brook flowed com¬ 
fortably by the barrier. The entire brook for several hundred feet 
has successively withdrawn more and more from its meanders by a 
combination of the partition and short-cut processes. 
Development of the partition plain .— A deflection of the current 
by any of the afore-named processes causes rapid erosion and the 
consequent widening of the channel. The river in struggling to with¬ 
draw rapidly from the opposite bank deposits on that side, and yet 
away from it, a sand bar which soon develops into an island. Con¬ 
tinued outward cutting by the thread of the current causes the river to 
withdraw more and more from its shallow bank (see text-figure D). The 
downward cutting of the thread of the current deepens the wider and 
stronger channel, thus drawing the water off from the more shallow 
channel. Erosion continues gradually until flood season, when suddenly 
more erosion takes place and much material is deposited, forming sand 
bars which part the river. As the current departs from its weaker chan¬ 
nel, this abandoned course and the one-time island are added to the 
growing partition plain; and the river has moved laterally an appre¬ 
ciable amount. 
The continued deflection of the current allows, at times of excessive 
flood, the formation of another and yet another sand-bar island, which 
upon the departure of the river from the weaker channels are succes- 
