152 FRAGMENTS OF SCIKNCE. 



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 tho 

 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, 

 ' 



