152 FRAGMENTS OF SCIENCE. 
center of the ancient river varied, being narrowest where 
that depth was greatest. 
The vast comparative erosive energy of the Horseshoe 
Fall comes strikingly into view when it and the American 
Fall are compared together. The American branch of the 
river is cut at a right angle by the gorge of the Niagara. 
Here the Horseshoe Fall was the real excavator. It cut 
the rock, and formed the precipice, over which the 
American Fall tumbles. But since its formation, the 
erosive action of the American Fall has been almost nil, 
while the Horseshoe has cut its way for 500 yards across 
the end of Goat Island, and is now doubling back to exca- 
vate its channel parallel to the length of the island. This 
point, which impressed me forcibly, has not, I have just 
learned, escaped the acute observation of Professor Ramsay.* 
The river bends; the Horseshoe immediately accommo- 
dates itself to the bending, and will follow implicitly the 
direction of the deepest water in the upper stream. The 
flexures of the gorge are determined by those of the river 
channel above it. - Were the Niagara center above the fall 
sinuous, the gorge would obediently follow its sinuosities. 
Once suggested, no doubt geographers will be able to point 
out many examples of this action. The Zambesi is thought 
to present a great difficulty to the erosion theory, because 
of the sinuosity of the chasm below the Victoria Falls. 
But, assuming the basalt to be of tolerably uniform tex- 
ture, had the river been examined before the formation 
of this sinuous channel, the present zigzag course of the 
gorge below the fall could, I am persuaded, have been 
predicted, while the sounding of the present river would 
enable us to predict the course to be pursued by the erosion 
in the future. 
But not only has the Niagara river cut the gorge; it has 
carried away the chips of its own workshop. The shale, 
being probably crumbled, is easily carried away. But at 
the base of the fall we find the huge boulders already de- 
scribed, and by some means or other these are removed 
* His words are: " Where the body of water is small in the 
American Fall, the edge has only receded a few yards (where most 
eroded) during the time that the Canadian Fall has receded from 
the north corner of Goat Island to the innermost curve of the 
Horseshoe Fall." Quarterly Journal of Geological Society, May, 
18o9. 
