188 J. D. Dana—The Flood of the Connecticut River Valley 
of the valley; and for the sake of an estimate and not an 
over-estimate, 75 feet may be the amount deducted. 
According to the section, the height above modern low-water 
level at Haverhill was about 260 feet; and this, diminished by 
75, gives for the depth 185 feet. So we obtain for Hanover 
and White River Junction, if the height of the intervening falls 
be divided between them, 295-75=150 feet ; for Windsor, 
216-75=141 feet; for Brattleboro, 210-75= 135 feet: for South 
Vernon, near the border of Massachusetts, 207-75=132 feet. 
may thence take for the average depth north of the Mas- 
sachusetts line, 140 feet. The depth on the southern boundary 
of Massachusetts obtained by the same method would be 125 
feet, and at Hartford in Connecticut, 125 feet. But the width 
is so much greater after entering Massachusetts, that it is quite 
certain, as already stated, that the less depth is more than bal- 
anced by the greater width. 
3. MEAN wiprH.—In order to obtain an approximation as to 
the mean width of the flooded stream between Wells River and 
the Massachusetts line, we may review, for a few localities, not 
only the width (which I take from Mr. Upham’s map), but 
also the areas of cross-sections. 
At Haverhill, the highest normal terrace of the east side rises 
nearly to its fall height, 263 feet above low water gee directly 
from the lower terrace-plain of 83 feet. The widt the chan- 
sea -way on the map, above the 88-foot terrace, is CE 000 feet. 
Taking for the depth of water 2683 —83=180 feet, the area of the 
cross section, with this width, would be 720, 000 square feet. 
Between northern Orford and Fairlee, 8 miles south of 
Haverhill, the higher terraces are wanting. Taking for the 
width only that covered by the valley deposits, that is, the low 
terraces—it is about 3,300 feet—which is too low, because there 
is no high terrace to mark the actual width, and the low ter- 
races referred to are only 55 feet above low water. The height 
e flood as given in the section, Plate 2, is 252 feet; thence, 
with the depth (252—55=) 197 feet, and with 3,300 feet as the 
width, area of cross-section is 650,000 square feet. 
Where the valley passes Norwich and Han nover, the most 
peaninent terrace has a height of about 150 feet above low 
water in the river, while the upper one, marking flood limit, is 
210 feet. The channel. -way has hence a narrow lower, and a wide 
upper section. For the width of the former, I have measure- 
ments obtained for me by Prof. R. Fletcher, of the School o 
Civil Engineering at Dartmouth College. The measurements 
were taken between points half-way up the steep terrace-front. 
600 feet below the bridge crossing the river, width : oe feet. 
400 feet above * 
soo t «Yao 
y 3 500 “i a o o ; 000 “ 
