DAVIS: RIVER TERRACES IN NEW ENGLAND. 323 



terrace its valley suggests a method by which a quantitative determina- 

 tion may be made of the ratios of sweeping, swinging, and degrading. 

 If numerous measures are taken of the difference of level between 

 adjacent terraces in a certain section of a valley, it maybe expected that 

 two groups of minimum differences should be found ; the group of 

 smaller values representing the deepening of the valley floor in the inter- 

 val between the down-valley sweeping of two successive meanders ; the 

 group of larger values representing the deepening between two succes- 

 sive swings of the meander belt. 



If measures of this kind were taken in different sections of a valley 

 system, it might be possible to determine from their variations whether 

 an even regional uplift or a tilting were chiefly responsible for the 

 activity of the river in carving its terraces, as the following considera- 

 tions will show. 



In the case of uniform uplift over a large area, let it be assumed that 

 the movement was rather quickly initiated, and then steadily continued 

 until it rather rapidly weakened at its close. We should then expect 

 that the terrace scarp marking the interval between two lateral swings 

 of the meander belt would be of greatest measure and relatively constant 

 in the lower course of the main river ; but the slow initiation of the up- 

 lift might possibly be recorded by a few low terraces at the top of the 

 series ; the slow close of the uplift and the very slow degradation of the 

 valley floor in later time might be recorded by a few terraces of lower 

 and lower scarps at the base of the series. If any terrace in the lower 

 course of the river could be followed up the valley, it would assume 

 a relatively higher and higher position in the series; for when the river 

 had in its lower course worn down its valley floor to a low grade at the 

 close of the period of uplift, there w T ould still be a considerable amount 

 of degradation permitted to the middle and upper part of the river. As 

 a result, the very low terraces at the base of the series near the river 

 mouth might gain a higher rank and a greater scarp height further up- 

 stream. If the terraces could be followed up to the headwaters of the 

 river system, they would become narrower and finally disappear in 

 single-scarped V-shaped valleys. So far as they could be recognized, 

 the upper members of a headwater series might correspond in date 

 to the basal members near the river mouth ; while the basal members 

 of a headwater series would decrease in scarp-height as they were 

 traced down-valley, until they at last merged iu the even flood plain 

 of the middle or lower river course. So many are the irregularities 

 of drift terraces that there has not to my knowledge been any sys- 



