91 
“The means of the measurements on the sections, along perpendiculars 
‘from the contour at the date of each survey, measured on a tracing of the 
(published map, give the following results for the Canadian Fall (Fig. 1) :-— 
33 years 8 years 41 years 
endingin endingin ending in 
1875. 1883, 1883 
ft. ft. ft. 
Mean aggregate recession along contour of 
2,000 feet, from B to Goat Island ... 80 ... — ... 114 
Mean aggregate recession along contour of 
IQO0 OMe ety BrtOy Ci — atresia ¢acciade scene eesti ae et (OO vac gen 
Mean annual rate of regression along the 
whole contour where a visible change 
Was! Clacremy hea NNN et eal PE MARE MM HMR nN 2 
Total maximum regression at the inner- 
most recess == SPIE Ga meee! RECE  MSCR mad Kose Wer ayim Ia} min peas 10. 
Annual rate of maximum regression = ... See LOR Oh Ge 
“The ‘ American’ Fall, measured in ten sections, gave a total mean reces- 
sion of 374 feet in the 41 years ending in 1883, which is at the rate of about 
10 inches per annum. 
“T do not know that I have seen any estimate attempted of the relative 
volumes of water passing over the two Falls. From such imperfect data as 
I have, referring to depth and swiftness, I should think that the rate of 
erosion for each Fall gave some approximation to the volume of water 
. 
NEW- YORK 
Lin, SHORE 
Cows Hf 
S o 
No 
SCALE OF FEET a? 
0% 
0 200 400 600 oS 
628 FT. TO THE INCH i 
be eed 
! 
Fig.2. 
& ey 
LUNA ISLET 
‘discharged over each ; that is to say, 2? feet per annum for the Canadian 
Fall, 2 foot per annum for the ‘ American’ Fall, would signify that the former 
pours over its brink three times as much water as the latter. 
“* At the rates of recession above shown it is evident that at no very remote 
age the two Falls were united in one when abreast of the point in Fig, 2 
marked ‘ New York Shore, and the entire width was about the same as 
that of the present Canadian Fall alone. Moreover, the mean width of the 
H 2 
