334 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



now the case with the Westfield, because it has cut clown upon a hai'd- 

 rock barrier in the trap-ridge notch ; and it is probably for this reason 

 that the lower section of Little river has swuug so broadly and opened 

 the extensive valley floor already described as forming the southern 

 part of the open basin east of Westfield. Naturally enough, then, the 

 enclosure of the broad valley floor on the south — where Little river is 

 alone responsible for the form of its border — is nearly everywhere a 

 single high-scarp terrace with numerous one-sweep or two-sweep cusps. 

 In other words, Little river is swinging on its present flood plain 

 more broadly than it has at any earlier time during the process of deg- 

 radation. Second, whenever the smaller stream becomes superposed 

 upon a rock barrier, its work in the next up-stream stretch proceeds 

 at its own rate, entirely independent of that of the master stream. 

 Hence the valley floor in such a stretch tends to widen and thus to 

 under-cut all the narrower flood plains formed in earlier stages of deg- 

 radation. This is the case with both the second and third sections of 

 the Little river valley. It has a well-opened valley floor usually enclosed 

 by single terrace scarps that rise to the full height of the upper 

 plain, so far as I have followed them. The simple scarps have well- 

 developed re-entrants and cusps, showing an active lateral swinging of 

 the stream at present grade, but not giving indication of an equivalent 

 swinging at any higher flood-plain level, and hence not giving support 

 to the opinion that the river is to-day of an enfeebled constitution. 



Valley of Saxtons River, Vermont. Saxtons river enters the Con- 

 necticut from the west at Bellows Falls, Vermont, and shows a beautiful 

 variety of terrace foi*ms for some three miles above its mouth. Figures 

 40 and 41, separated by an unrepresented interval of about half a 

 mile, give rough illustration of these features. Careful survey would 

 undoubtedly show that the sketch-maps need many changes in de- 

 tails, but it is believed that the relative positions of terraces, with 

 their free and defended cusps, are shown with sufficient accuracy for 

 the purposes of the present discussion. The chief points here illus- 

 trated are as follows : — 



Western Section. In the up-stream or western section, Figure 40, 

 there are numerous ledges, but none of them have acted as local base- 

 levels. The present valley floor is graded with respect to a heavy rock 

 barrier a little east of the limit of Figure 40, and at the western border 

 of Figure 41. In the three strong ledges, M, Q, R, Figure 40, on the 

 north side of the valley, the rocks are schists, with strong dip to the 

 northeast, and hence with bold outcrops to the southwest. The stream 



