226 H. L. FAIRCHILD PLEISTOCENE MAHINE SUBMERGENCE 



latitude about 44° 17', which is precisely the figure that Upham gives 

 for his "normal" terrace at that point. 



DELTAS 



The most conspicuous features in the northern part of the "lower" 

 valley (the section forming the boundaiy between Vermont and New 

 Hampshire and south of the mouth of the Passumpsic EiA'er) are the 

 high sand plains, the deltas of tributary streams. In some stretches it is 

 possible that the valley was filled clear across except for the current chan- 

 nel. In such cases the water would have been a true river, but prac- 

 tically at the level of the standing waters below. 



Upham says of the deltas: 



"Tributary streams . . . frequently formed extensive deposits, . . . 

 similar in material to the floodplain in the main valley, but having a greater 

 height. Sometimes these deltas, being partially undermined, form conspicu- 

 ous terraces a hundred feet above the highest normal terrace, which is the 

 remnant of the river's continuous floodplain" (page 16). 



Several of the heavier deltas are well described by Upham: of Wells 

 and Ammonoosuc rivere, at Wells Eiver and Woodsville (page 29) ; at 

 mouth of Jacobs Brook, in Fairlee and Oxford (pages 33, 34) ; Mink 

 Brook, at Hanover (page 38) ; Lulls Brook, at Hartland (page 41) ; 

 Little Sugar, Black and Williams rivers (page 51) ; Black Eiver (page 

 52) ; Cold and Saxtons rivers, below Bellows Falls (page 54) ; at North- 

 field, Massachusetts (page 57). 



Upham's explanation of the great discrepancy between the height of 

 the "normal" terrace and the "tributar}^" delta terrace is that "the accu- 

 mulation was too great to be cleared away by the current in the main 

 valley'^ (page 33). Dana criticised this hanging up of the side deltas so 

 far above the main stream, and he took the summit of the deltas as 

 marking the flood level; but his gain in consistency in the genesis of 

 the deltas was overbalanced by the inconsistencies and dijEculties in- 

 volved in assuming such an immense flood (American Journal of Science, 

 volume 23, page 96). 



The form of some of the tributary deltas is evidence that they were not 

 built into a river having the strong flow that the assumed gradient would 

 demand. Built in a vigorous river, the deltas would be chiefly developed 

 on the down-stream side, in this case on the south side of the mouth of 

 the tributary. This is not apparent. But it is true that the most effect- 

 ive winds were from the north, and the cui're^ts due to winds and water 

 supply toward the south. Moreover, with the lifting of the land and 



