340 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



open section of the valley is enclosed by a high free cusp, C, at whose 

 apex the river is now working. Another open valley floor, I), 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 down the east side of the 

 valley past the entrance of Cold river, R, 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. 1 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 Tie 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 downstream from J. 



