Davis — Terraces of the Wesifield River ^ Mass. 89 



The flight of nine terraces in the Pochassic reentrant, above 

 described, constitutes the best series in the valley, as far as I 

 have seen it. Closer study will probably increase the number 

 of steps. The subeqnal height of the scarps suggests that these 

 terraces record nearly every northward swing of the river in 

 their locality. A similar number of swings has probably 

 occurred elsewhere ; the record of them is incomplete or want- 

 ing only because of the absence of defending ledges. It may 

 therefore be concluded in general that it is only in localities 

 well provided vrith ledges that one may expect to see preserved 

 in terraces the lateral remnants of all the flood plains that were 

 formed by the swinging river during the excavation of its 

 valley ; and that the maximum number of steps in a terrace 

 flight is only the minimum number of lateral swings made by 

 the river. All of these terraces testify to the graded condition 

 of the degrading river at the time the terrace plains were made. 

 The nine chance samples of river condition thus preserved may 

 be fairly taken to show that the degrading river was meander- 

 ing and swinging at grade during the whole period of terracing 

 in this section of the valley. There is no indication that the 

 individual terraces depend in any Avay whatever on individual 

 uplifts. 



12. Terraces south of the 'river. — The terraces on the south 

 side of the valley may now be considered. No ledges are seen 

 on this side of the river within the two-mile stretch included 

 in figure 6. The first ledges are found half a mile further 

 west ; they defend the eastern or down-valley side of a strong 

 reentrant a little west of the town farm. Correlated with the 

 prevailing absence of ledges is the absence of upper terraces. 

 The high plain is habitually bordered by a strong scarp of 

 forty or more feet, beneath which there may be several low 

 terraces; but in one case the low flood plain of the present 

 river enters a strong reentrant, P, to the base of single scarp 

 by which the whole descent is made from the high plain. 

 Nowhere in this district is there a flight of low-scarped terraces 

 from the top to the bottom level on the southern side of the 

 valley. The reason for this contrast between the two sides of 

 the valley may be with confidence ascribed to the ^^eneral south- 

 ward shifting of the belt within which the river swings, because 

 of the southward slope of the ledges on the north side of the 

 valley and the undefended condition of the terrace drift on the 

 south side of the valley. It is a sort of monoclinal shifting of 

 a river course. The several low terraces on the south might 

 seem at first to contradict this explanation. They may, how- 

 ever, be reasonably explained as being not yet swept away. 

 The river cannot attack the whole length of the southern side 

 of the valley at once ; it will swing against the southern 



