68 F. B. TAYLOR—ORIGIN OF GORGE OF WHIRLPOOL RAPIDS. 
been propagated up stream rapidly to the first resisting ledge of rocks in 
the path of the river, and this took place at each step in the progress of 
_the lowering. <A bank of drift could not endure more than a few minutes; 
or, at most, a few hours, with so great a volume of water pouring over it 
as a cataract or rushing over it with the fury of the rapids. It follows 
that with the lowering of the thin wall there came into existence almost 
simultaneously a new cataract at some point higher up. As the wall 
broke down and the water above fell the new cataract grew in height. 
At first it was low, a mere swell, then a cascade, and finally a cataract. 
As soon as it had developed sufficient force by the power of its fall it 
began gorge-making on its own account. 
At the place of the crumbling wall below an opposite change went on 
simultaneously. With the gradual lowering of the wall this cataract lost 
its power and stopped, or, at least, greatly diminished its work of under- 
cutting. This virtually stopped its recession, and the wall was hence- 
forth removed mainly by wearing and breaking off at the top—a slower 
process—and the lower the wall became the more slowly it wore away. 
While the thin wall was wearing down the new cataract was retreating, 
cutting slowly and not deeply at first, because it fell only a few feet, but 
with the lowering of the water at its foot it gained power and gradually 
took on the character of the great cataract that had cut out the Cove sec- 
tion. The cutting away of the thin wall at the lower side of the Whirl- 
pool must have been effectually checked when the hard bed of the quart- 
zose sandstone was reached. This layer probably formed for a long time 
the sill over which the water made a moderate cascade, but at length it 
was broken through. The foundation of the thin wall is still there, and 
it is over this that the river makes its sharp, swift descent just below the 
Whirlpool. 
Upper Shoal ledge.—When it encountered the drift-filled Saint Davids 
gorge the cataract was shifted with relative suddenness from the Cove 
section to some point above the Whirlpool substantially in the man- 
ner described above. Where was the new cataract? Did the old Saint 
Davids gorge end at the south side of the Whirlpool or did it extend 
up to the south side of the Eddy basin; or did a small creek ravine ex- 
tend still farther up, where the gorge af the ate ee rapids is now, 
to the lower end of the Upper Great gorge? 
This brings us to the most important and critical point in the Niagara 
problem, so far as it can be interpreted from the study of gorge characters 
alone. The solution of the problem of the origin of the gorge of the 
Whirlpool rapids depends mainly on the answer to the question, What 
is the age of the Eddy basin? If this basin is a part of the preglacial 
Saint Davids gorge, then, so far as can be inferred from the study of the 
a 
