igoo-i.] On the Ancient Drainage at Niagara Falls. 13 



however, as at present in front of the American fall, the great rock 

 masses are now piled up close to the cliff in such a way as effectually to 

 stop the water from wearing away the soft shale. 



The deep channel being in this way partially filled, the action of the 

 weather on the lateral walls gradually causes a talus to be deposited on 

 the sides of the gorge, giving the older parts of the river the rough 

 V-shape shown by the soundings taken at the Cantilever bridge. 



One more thing remains to be accounted for, viz., the Whirlpool. 

 Where the current from the Whirlpool rapids enters the Whirlpool, a 

 ledge of rocks projects from the east bank into the Whirlpool. The 

 appearance of the water indicates a shallow part, probably a continua- 

 tion of the ledge, running clear across to the other side. The Whirlpool 

 basin itself is very deep, probably deeper than it was worn by the Falls 

 or by the pre-glacial stream which formerly passed here. Where the 

 water leaves the pool the passage is very narrow, rocks in place project- 

 ing into it both from the Canadian and American sides. Even in the 

 centre of the channel the water appears to be quite shallow. 



The depth of the water in the pool is due to the course of the river. 

 Even while it ran on the top of the bank, before the Falls reached the 

 Whirlpool, there would be here a deep pond, in character much the 

 same as the present one. After the Falls passed this point, the same 

 cause would deepen the hole where the change in direction of the 

 stream occurred. 



The shallowness of the exit of the Whirlpool is comparatively easy 

 to account for. As the Falls cut their way back from Queenston, a 

 time would come when only a very thin wall would remain between the 

 water of the Whirlpool and that of the gorge. As this partition would 

 break down rapidly in its upper part, the level of the Pool would 

 suddenly lower, leaving the last part of the quartzose sandstone to be 

 eroded only by the mechanical force of the running water — a very slow 

 process. 



The ledge above the Whirlpool was left during the time that the 

 thin wall below was being taken out, before the cataract at the upper 

 part had attained power enough to excavate deeply. 



The Whirlpool basin was then probably no deeper than the Medina. 

 Since then, the peculiar character of the motion of the water and the 

 erosive action of the stones and pebbles carried by it, have deepened 

 the basin to its present depth. 



