* 
198 J. D. Dana—The Flood of the Connecticut River Valley 
We thence have 1:25 feet per mile (=50 seconds nearly in 
angle) as the mean rate of change northward along the Connec- 
ticut valley. 
e line D S on the section (figure 2, Plate 2) represents the 
‘mean-tide level thus deduced. It is drawn from a point on the 
Sound marking 25 feet above mean-tide level (supposing the 
change on the Sound to be 25 feet, though along by the mouth 
of the Connecticut it may not have exceeded 15 feet), and rises 
in the direction of the valley northward, at the rate of 1-25 feet 
per mile. 
It cannot be assumed that the rate was equable throughout 
the valley. It may have been less than the deduced rate to 
b. Effects of the change while the river was low.—It the river 
were, for a while, at or near modern low-water level (and it 
probably was so), the change of 1:25 foot a mile, would have 
taken out all the mean slope from the several parts of the 
valley, excepting the abrupt descents at the falls. The tides 
would have extended beyond the Holyoke dam, eight miles 
above Springfield, obliterating the falls and have stood 15 
feet above its top; and have reduced Turner’s Falls nearly 30 
feet in height. The elevation of low-water level above the sea 
would have been only 35 feet at South Vernon, or the Massachu- 
setts boundary; at Windsor, 83 feet; at Haverhill, 120 feet. 
Hence the descent between South Vernon and Windsor would 
have been only 48 feet, which is three feet less than the fall (51 
feet) at Bellows Falls, situated between these two points ; and 
the descent between Windsor and Haverhill would have been 
only 87 feet, which is three feet less than the fall (40 feet) at 
the falls between Hanover and White River. Since these falls 
would have wasted, by friction at bottom, any velocity which 
might have been gained by descent, the Connecticut River 
would have been for the most part a series of nearly still-water 
stretches with falls at a few distant points. This condition 
would have continued, with but little change as to the effect 0 
the dams, after the waters had risen 20 to 25 feet above low . 
water, as in a modern floo 
