28 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
and often the river has swung broadly away from it. The old plain is 
more wavy than undulating. The sand bars and the intervening 
channels are no longer distinct. It is difficult and practically impossi¬ 
ble to define the positions of the courses from which the river suc¬ 
cessively departed. It is probable that the plain will be elevated above 
the river which, since the formation of this plain, has degraded to 
lower and lower levels, forming younger and lower plains. Such 
elevated old partition plains will show signs of weathering and dis¬ 
section. 
As a result of these processes, two types of terrace plains are con¬ 
structed, the meander built and the partition built. The first type 
is formed by the regular deposition at the inner and lower side of the 
down-stream sweeping meanders. Such a terrace is even and nearly 
level, sloping gently toward the meander, and is the type generally 
recognized as the normal flood plain. A second constructive type is 
produced by the partition process. A terrace so formed slopes gently 
toward the river, but is undulating, with elevations and channel-like 
depressions, representing the former islands and the intervening 
deserted channels. The other processes of lateral movement check 
deposition in one place to start it elsewhere. They straighten the 
river locally, and by destroying the existing curves, deflect the current, 
forcing it to establish a new systematic series of meanders. The new 
deflection of the thread of the current withdraws the stream from 
former erosion banks by the deposition of a series of sand-bar islands, 
leaving partition plains. 
Terraces of the West River Valley. 
Terrace pattern, early stage .— Terraced valleys show different stages 
of development: the early stage, the middle stage, and the late stage, 
corresponding to the stages of youth, maturity, and old age. In the 
early stage, the river valley has commonly but one or two terraces, 
perhaps one completed terrace and one low flood plain. They show 
clear cut, simple forms, few in number, wide in extent. The terrace 
pattern is without the complexities of middle life and has the most 
immature development of terrace drainage, if any. Any terracing 
brook furnishes a good example of this early stage, showing forms 
