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 may be 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 would 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 leadwater series would decrease in scarp-height as they were 
traced down-valley, until they at last merged in 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- 
