340 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
open section of the valley is enclosed by a high free cusp, C, at whose 
apex the river isnow working. Another open valley floor, D, follows the 
free cusp, and is limited by a second free cusp, E, of less height but of 
greater forward reach than the first, The meaning of these two free 
cusps will be considered below. 
Returning to Bellows Falls and following doen the east side of the 
valley past the entrance of Cold river, k, from the northeast, ledges are 
found to be more numerous. A broad mid-height terrace was opened 
until a ledge, F, was discovered in the base of the uppermost terrace 
just south of the Alstead road ; the further southward extension of the 
high terrace has not been followed. The mid-height terrace, followed 
by the upper north-and-south road, was cut back by a much later swing 
of the river near present flood-plain level, until a high ledge, G, was dis- 
covered an eighth of a mile south of Cold river : the lower north-and-south 
road skirts its base. Nearly a mile further south is a group of admir- 
ably defended terrace cusps, H, up-valley from which the river has swept 
out some vigorous curves, and on one of which — where the mid-height 
terrace first advances near the Fitchburg railroad — the river was nearly 
superposed ; the rapids that occurred here for a time were abandoned 
as the river slipped off the northwest slope of the ledges. Near this 
point the lower terrace advances to the river bank, on account of 
the farther forward reach of other ledges, J; one of them now out- 
crops in the river bank and thus insures the enduring protection of 
at least part of the low plain on which the railroad is here laid.! It 
is thus evident that the meander belt of the river has here been 
constrained to take a more and more westward course as it cut 
deeper and deeper; and it is probably on this account that the first 
large western re-entrant below Saxtons river has been so thoroughly 
scoured out at a low level. 
The lower eastern terrace is gradually cut back down-valley from 
the foremost defending ledge; and a broad low plain, K, is thus 
opened to a half-mile width, after which it narrows towards the 
bridge between Walpole (W) and Westminster (X). The mid-height 
terrace continues down-valley from the abandoned rapids, first show- 
ing an apparently free two-sweep cusp; then a defended cusp, L, the 
defending ledge of the latter being disclosed in a shallow railroad 
cut at the base of the terrace; after this the terrace is cut some 
1 The shading to indicate a low terrace along the east bank of the river is acci- 
dentally omitted in Figure 41 for three-fourths of an inch up-stream and half an 
inch down-stream from J. 
