27 



of importance. The extra width was due partly to 

 the augmented volume of the river (by water coming 

 directly from the ice sheet) as compared with the present 

 volume, and partly to the wide, flat rock floor above the 

 falls, which caused the water sheet to be spread to unusual 

 width. This last condition led to the formation of Winter- 

 green terrace and the associated lower rock terraces. The 

 shallowness to the head of Foster's flat was caused mainly 

 by the fact that Lake Iroquois stood 125 feet (38 m.) 

 higher than the present level of Lake Ontario and backed 

 up into the gorge at this level. The original narrowness and 

 shallowness of the Old Narrow gorge just below must 

 have tended to contribute to the same result until it was 

 cut down by the scour of the rapids. The same uplift that 

 raised the Kirkfield outlet sent the augmented discharge 

 of the upper three lakes to Niagara, and it was then that 

 the large-volumed cataract first began gorge making at 

 the bend below the university. It also raised Lake Iro- 

 quois about 40 feet (12 m.), or from about 85 feet to 

 125 feet (25 to 38 m.) above present lake level. When 

 Lake Iroquois fell to a lower level, the water at the base 

 of the falls fell, and the falls immediately became in effect 

 higher and bored deeper. This change occurred when 

 the falls were at the head of Foster's flat, for, from this 

 point up to the upper side of the Eddy basin the river is 

 deep. Spencer's soundings show depths of nearly 100 

 feet (30 m.) in the stretch between the whirlpool and 

 Foster's flat. 



The reef which produces the sharp rapids at the 

 outlet of the whirlpool owes its origin to the breaking away 

 of the east wall of the whirlpool before the vertical fall had 

 time to carve out the sandstone at its base. When the 

 break in the wall came the lowering of the water in the 

 whirlpool must have been quite rapid. Then, continuing 

 their work, the falls cut out the Eddy basin before the 

 volume of the river was reduced. In the lake history, 

 this section is the correlative of the Port Huron stage of 

 Lake Algonquin. 



The Gorge of the Whirlpool Rapids. 



This section is about three-fourths of a mile long and 

 extends from the upper side of the Eddy basin to the head 

 of the narrows just above the railway bridges. The 



