21 



At a later time the great ice barrier which spanned 

 the St. Lawrence valley somewhere below Kingston and 

 held Lake Iroquois up to the level of the Rome outlet, 

 disappeared and the lake was drained off. The waters 

 in the Ontario basin then fell much below the present 

 level of Lake Ontario. This change revived the down- 

 ward cutting of Niagara river, and the older parts of the 

 gorge were then deepened by a moderate amount, but this 

 was accomplished chiefly by the wearing action of rapids 

 rather than by the boring of vertical falls. The effects 

 of both the higher and lower stages of the waters of the 

 Ontario basin upon the falls are seen in the gorge from its 

 mouth up to the head of Foster flats. 



Soundings in the Niagara gorge. 



The U. S. Lake Survey made a number of soundings 

 in Niagara river many years ago, but these were all con- 

 fined to the upper great gorge from a point opposite the 

 American Falls down nearly to Swift Drift point. All 

 the other soundings within the gorge were made by Dr. 

 Spencer, some of them under conditions of great difficulty. 

 He made three attempts to sound the depth of the water 

 at the base of the Horseshoe falls with two carefully pro- 

 tected Tanner-Blish sounding tubes. One of these attempts 

 failed, but two of them appeared to be successful and he 

 gives the results as 69 and 72 feet (21 and 21.9 m.) respect- 

 ively. Considering the tremendous turbulence of the 

 water at the base of the falls, however, there seems to be 

 some doubt as to what might happen to the apparatus 

 there. It seems quite as likely that it might be carried 

 backward under the falls so as to strike the wall under 

 the over-hanging ledge as that it should strike the bottom. 

 Three soundings made at the head of the Whirlpool rapids 

 give depths of 52, 86, and 68 feet (15.8, 26.2 and 20.7 m.) 

 going eastward from the west side, and may be correct, 

 but there is considerable possibility of error in this case 

 also. The principal soundings will be referred to in the 

 description of the gorge sections. 



