214 'FRAGMENTS OF SCIENCE 



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 text- 

 ure, 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 Kiver 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 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 transporting agent. Probably it is so to 

 some extent. But erosion acts without ceasing on the 

 abutting points of the bowlders, thus withdrawing their 

 support and urging them gradually down the river. Solu- 

 tion also does its portion of the work. That solid matter 

 is carried down is proved by the difference of depth be- 

 tween the Niagara Eiver and Lake Ontario, where the river 

 enters it. The depth falls from 72 feet to 20 feet, in con- 

 sequence of the deposition of solid matter caused by the 

 diminished motion of the river. 1 



The annexed highly instructive map has been reduced 



1 Near the mouth of the gorge at Queenston, the depth, according to the 

 Admiralty Chart, is 180 feet; well within the gorge it is 132 feet. 



