NATURAL HISTORY, TORONTO REGION
visit of Sir Charles Lyell in 1842, and many papers have been written on the subject. The most important contributions to the literature have been made by Gilbert, Spencer and Taylor, who do not entirely agree as to the succession of events.
All agree that the falls began at the Niagara escarpment near Queenston on the Canadian side and Lewiston on the American when the ice of the Ontario lobe had so far withdrawn as to set free a large part of the basin. It is probable that the falls began as three separate plunges over the three harder rock layers of the escarpment, the Cataract sand-stone, the Clinton limestone and the Niagara (Lock-port) limestone. The upper limestone is the thickest and most resistant of the three beds, so that ultimately the two lower falls worked their way back to the upper fall, probably at Niagara Glen; since then there has been only one fall.
The Niagara gorge is 300 feet deep at Queenston Heights, but diminishes to 158 feet at the Canadian or Horseshoe Fall. Dr. Spencer has sounded below the falls, finding a depth of water of 192 feet, making a total depth of 340 feet for the chasm.
The width of the gorge varies to an important degree, having two stretches which are narrower than the rest, at Niagara Glen and just below the railway bridges, both accompanied by powerful rapids. These narrower portions may be accounted for by supposing the greater part of the drainage of the Upper Lakes to be diverted to the Trent Valley