SOME OBSERVATIONS ON NIAGARA. 



225 



its course, from Lewiston Heights to its present position, the form of 

 the fall was probably that of a horseshoe ; for this is merely the expres- 

 sion of the greater depth, and consequently greater excavating power, 

 of the centre of the river. The gorge, moreover, varies in width as 

 the depth of the centre 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 to- 

 gether. The American branch of the upper 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 doub- 

 ling back to excavate a channel parallel to the length of the island. 

 This point, I have just learned, has not escaped the acute observation 

 of Prof. Ramsay. 1 The river above the fall bends, and the Horse- 

 shoe immediately accommodates itself to the bending, following im- 

 plicitly the direction of the deepest water in the upper stream. The 

 flexibility of the gorge, if I may use the term, is determined by the 

 flexibility of the river-channel above it. Were the Niagara above the 

 fall far more sinuous than it is, 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, had the river been ex- 

 amined 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 crum- 

 bled, is easily carried away. But at the base of the fall we find the 

 huge bowlders already described, and by some means or other these 

 are removed down the river. The ice which fills the gorge in winter, 

 and which grapples with the bowlders, has been regarded as the trans- 

 porting agent. Probably it is so to some extent. But erosion acts 

 without ceasing on the abutting points of the bowlders, thus with- 

 drawing their support, and urging them gradually down the river. 

 Solution also does its portion of the work. That solid matter is car- 

 ried down is proved by the difference of depth between the Niagara 

 River and Lake Ontario, where the river enters it. The depth falls 



1 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 Horse- 

 shoe Fall." Quarterly Journal of the Geological Society, May, 1859. 

 vol. in. 15 



