THE HISTORY OF THE NIAGARA RIVER. 241 



vertical plane runuing a little west of south, or parallel to the direction 

 of greatest incliuatiou of old water-plaues. At N is represented the 

 Niagara escarpment and the associated slope of the lake basiii; at A 

 the Adirondack Mountains. R and T are the passes at Rome and at 

 the Thousand Islands. Successive positions of the ice front are marked 

 at I', P, and P. The straight line numbered 1 represents the level of 

 lake water previous to the origin of the Niagara River; 2 gives the first 

 position of the water level after the establishment of the Home outlet ; 

 and the level gradually shifted to 3; 4 is the first of the series of tem- 

 porary water levels when the water escaped between the mountain 

 slope and the ice front; 5 represents the first position of the water level 

 after the occupation of the Thousand Island outlet ; and 6, the present 

 level of Lake Ontario. 



It should be added parenthetically that the shore of Lake Iroquois 

 as mapped in PI. il is not quite synchronous. Between 2 and 3 of PI. 

 Ill there was a continuous series of water levels, but it was not easy to 

 map any one except the highest. The northern part of the map delin- 

 eates the margin of water level 2 and the southern part the margin of 

 water level 3. 



It is easy to see that these various changes contribute to modify the 

 history of the Niagara River. In the beginning, when tlie cataract 

 was at Lewiston, the margin of Lake Ontario, instead of being 7 miles 

 away, as now, was only 1 or 2 miles distant, and the level of its water 

 was about 75 feet higher than at present. The outlet of the lake was 

 at Rome, and while it there continued there was a progressive change 

 in the attitude of the land, causing the lake to rise at the mouth of the 

 Niagara until it was 125 feet higher than now. It fairly washed the 

 foot of the cliff at Queenstou and Lewiston. Then came a time when 

 the lake fell suddenly through a vertical distance of 250 feet, and its 

 shore retreated to a position now submerged. Numerous minor oscil- 

 lations were caused by successive shiftings of the point of discharge, 

 and by progressive changes in the attitude of the land, until finally the 

 present outlet was acquired, at which time the Niagara River had its 

 greatest length. It then encroached 5 miles on the modern domain of 

 Lake Ontario, and began a delta where now the lead-line runs out 30 

 fathoms. 



While the level of discharge was lower than now, the river had dif- 

 ferent powers as au eroding agent. The rocks underlying the low 

 plain along the margin of the lake are very soft, and where a river 

 flows across yielding rocks the depth to which it erodes is limited 

 cliiefiy by the level of its point of discharge. So when the point of 

 discharge of the Niagara River — the surface of the lake to which it 

 flowed — was from 100 to 200 feet lower than now, the river carved a 

 channel far deeper than it could now carve. When afterward the rise 

 of land iu the vicinity of the outlet carried the water gradually up to its 

 present position in the basin this channel was partly tilled by sand and 

 H, Mi8. 129 16 



