344 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
the southern part of Springfield there are several ledges and some ex- 
posures of bouldery till, by which the opening of the valley to the east 
has been restrained, and a little further south, by the mouth of Pecowsic 
brook, a strong ledge deflects the river to the southwest. 
No ledges are found in the terrace scarps on the western side of the 
valley hereabouts, although several rather well-formed cusps project 
forward towards the river: one at the grounds of the Country club; 
another at the old Meeting-house north of West Springfield and a third 
between West Springfield and the Agawam. The Westfield river 
enters the main valley in the re-entrant between the second and third 
cusps, while south of the third cusp the Connecticut has repeatedly 
scoured out re-entrants from which it has been withdrawn by short-cuts 
or cut-offs. I am inclined to think that the Connecticut has been 
pushed eastward by the action of the Westfield ; that it has therefore 
repeatedly swung westward from the Pecowsic ledges, and that the 
Agawam re-entrants are thus to be explained. If so, they fall into the 
same class with those of the Westfield in the re-entrant next west of 
the trap-ridge notch (page 330). The southernmost of the three free 
cusps on the west side of the Connecticut valley, below the entrance of 
the Westfield, would thus correspond with the free cusp on the south 
side of the Westfield, below the entrance of Little river. The other free 
cusps of the Connecticut may perhaps come to find an explanation in a 
process similar to that suggested for the free cusps between Bellows 
Falls and Westminster (page 341). 
There is nothing in this stretch of the river to suggest a significant 
diminntion of volume since terracing began. The frequent occurrence of 
high single scarps would on the other hand suggest that the river is 
to-day demanding a breadth of swinging as great as or greater than it 
ever did before. 
Tue MERRIMAC BETWEEN ConcorpD AND MancuHester, N. H. ‘The 
Merrimac, near Concord, has opened a broad flood plain, on which a 
number of former meanders are now represented by ox-bow lakes. On 
the east the plain is commonly bounded by a single high scarp, which 
the river is actively under-cutting at one point. On the west there is a 
single high scarp bordering part of the plain north of the city ; but a 
few ledges appear, and the scarp is divided into several terraces as the 
city is entered. Passing down the valley (southward) ledges appear more 
frequently, the breadth of the flood plain gradually decreases, and ter- 
races appear in increasing numbers. The valley about Concord is one 
of the best examples for illustration of the capacity of an unconstrained 
