170 
The AmerlcAni Geolo'jisi. 
Marcli,1895 
111 iniu}2; those above, iind this depends, other thiiij^s l)eiiig equals 
upon the liight oi' tlie falh It is true that the liiglier the fall 
the greater its power to cut downward. But by the resist- 
ance of the rocks at the bottom and the consequent deflection 
^TLg-an Qorq'e.. 
Fio. :{. 
of forces in strong currents the power to cut laterally is also 
increased. For a cataract circumstanced like Niagara the 
law is the veiy reverse of that for rivers flowing without 
cataracts, namel}^, the volume of the river and the geological 
structure remaining the same, the higher the cataract the 
wider the gorge. 
It is interesting to compare the gorge of the present period 
of Niagara with the channel of the rapids at Sault Ste. Marie. 
Since the abandonment of the Nipissing outlet, Niagara has 
cut back its gorge nearly two miles. But the Sault, which has 
probabl}' been open half as long, has no visible recent rock 
gorge, or, if there is any, it is submerged. Of course there 
are many different elements to take into account. But even 
when a liberal allowance is made for all circumstances which 
might cause Niagara to cut back more rapidly and the Sault 
less rapidly, it still remains a fact that the difference between 
their amounts of cutting is so great that it demonstrates the 
younger age of the Sault. The inference from this fact 
should be put alongside of that drawn from tlie character of 
the Superior beaches. The beaches prove that the northward 
uplift was extremely gradual and even in its action, while the 
Sault without a gorge suggests that the barrier whicli holds 
up lake Superior was not uncovered until a considerable time 
after Niagara liad replaced the Erigan river. But on the 
other hand, the submerged Sault beach in the Superior basin 
proves that the barrier had been uncovered some time before 
