GEOLOGY. 613 



and forms a cave behind the fall, in which persons can 

 enter on the Canadian side, and pass by a rough path to- 

 ward Goat Island. 



The sound of the fall varies with the condition of the at- 

 mosphere and the wind. Frequently it can be heard only a 

 short distance, and again it rolls over the land to the shores 

 of Lake Ontario, and across its waters to Toronto, forty-six 

 miles distant. At the edge of the abyss it is heard in full 

 force, a deep, monotonous rumbling, like the machinery of 

 a thousand great mills. 



In the deep chasm below the fall, the current, which is 

 less than 1000 feet in width at that point, forms great 

 whirlpools and eddies. Dangerous as it may appear, the 

 river is here crossed by small boats, and a small steamboat, 

 called the Maid of the Mist, takes passengers nearly to the 

 foot of the falls. On each side of the gorge the walls rise 

 almost perpendicularly from the fragments piled along their 

 base, and access to and from the summit can be had only by 

 means of stairways constructed at several points. Within 

 two miles of the falls is the wire suspension bridge, thrown 

 across the gorge at the height of 258 feet above the water, 

 and supported by towers upon each bank, the centres of 

 which are 800 feet apart. The current here is about 350 

 feet wide. The bridge was constructed in 1855 by Mr. 

 Roebling for the passage of railway trains, and twenty- 

 eight feet below the railway it also sustains a carriage and 

 a foot track. 



The gorge through which the Niagara River flows below 

 the falls, amounting, at the terrace, to about 3G6 feet in 

 depth, bears striking evidence of having been excavated by 

 the river itself. Moreover, observations taken during the 



