DISCRIMINATIVE CRITERIA 195 



were not glacial; but we do have the positive proof that an estuary 

 occupied the trunk valley at the altitude of the Catskill delta, with a 

 splendid bar at Hudson Village, on the east side of the open valley, at cor- 

 responding elevation (84, page 290) . In practically every tributary valley 

 on both sides of the Hudson-Champlain, from New York City to Canada, 

 we find delta plains in precise agreement with the uptilted water phme 

 of the open valley. Such correspondence in level in a multitude of in- 

 dependent water bodies would be impossible. Glacial deposits at higher 

 levels are often recognized. The Catskill delta is simply one of very 

 many estuarine features in accordance through 300 miles of uplifted 

 territory. Most geologic reasoning is based on the kind of cumulative 

 evidence which we have in this case. 



It is possible that a few high-level features regarded by the writer as 

 marine level may be glacial; but they are certainly exceptional. The 

 deltas and shore features marking the stand of the sea on the depressed 

 land occur in every one of the hundreds of valleys opening to the sea. 

 In the tracing of the marine plane many features have been ignored 

 because of some doubt. 



TERRACES 



It is important to discriminate the terraces formed in subsiding static 

 waters from the benchings on stream-cut valley sides. That this has not 

 always been done is shown by the reference of terraced estuary deposits 

 to river work. The successive banks of rejuvenated streams may repre- 

 sent fioodplains that were aggraded much above the highest static water 

 level, both in horizontal and vertical distance. The genetic distinction 

 is necessary for the clear recognition and close determination of the sum- 

 mit marine plane, although for long distances over the great uplifted 

 area even the superior stream benches are useful in indicating approxi- 

 mate levels. The description of a typical example will illustrate the topic. 



At Littleton, IsTew Hampshire, the valley of the iimmonoosuc, a tribu- 

 tary of the Connecticut, is about one-fourth mile wide. Horizontal 

 benches are conspicuous on both sides of the narrow valley. The main 

 street of the village is on the north side main terrace. On the south side 

 tliree benches occur, shown in the photograph, plate 9. These benclies 

 are partly erosional, cut in the till, and partly constructional as flood- 

 plain deposit. The constriction of the valley rides out efficient wave 

 action. It is apparent that the river flow -was up to the highest bench, 

 some 10 to 15 feet above the railroad station, whicli is given as 772 feet, 

 and that the lower lines were produced as the river fell in adjusting itself 

 to a falling baselevel. 



