to be taken into account. Boulders derived from the adjacent cliffs
visibly cumber the sides of the river. Against these the water rises
and sinks rhythmically but violently, large waves being thus produced.
On the generation of each wave, there is an immediate compounding of
the wave-motion with he river-motion. The ridges, which in still
water would proceed in circular curves round the centre of
disturbance, cross the river obliquely, and the result is that at the
centre waves commingle, which have really been generated at the sides.
In the first instance, we had a composition of wave-motion with
river-motion; here we have the coalescence of waves with waves. Where
crest and furrow cross each other, the motion is annulled; where
furrow and furrow cross, the river is ploughed to a greater depth; and
where crest and crest aid each other, we have that astonishing leap of
the water which breaks the cohesion of the crests, and tosses them
shattered into the air. From the water level the cause of the action
is not so easily seen; but from the summit of the cliff the lateral
generation of the waves, and their propagation to the perfectly
obvious. If this explanation be correct, the phenomena observed at
the Whirlpool Rapids form one of the grandest illustrations of the
principle of _interference_. The Nile 'cataract,' Mr. Huxley informs
me, offers more moderate examples of the same action.

At some distance below the Whirlpool Rapids we have the celebrated
whirlpool itself. Here the river makes a sudden bend to the
north-east, forming nearly a right angle with its previous direction.
The water strikes the concave bank with great force, and scoops it
incessantly away. A vast basin has been thus formed, in which the
sweep of the river prolongs itself in gyratory currents. Bodies and
trees which have come over the falls, are stated to circulate here for
days without finding the outlet. From various points of the cliffs
above, this is curiously hidden. The rush of the river into the
whirlpool is obvious enough; and though you imagine the outlet must be
visible, if one existed, you cannot find it. Turning, however, round
the bend of the precipice to the north-east, the outlet comes into
view.

The Niagara season was over; the chatter of sightseers had ceased, and
the scene presented itself as one of holy seclusion and beauty. I
went down to the river's edge, where the weird loneliness seemed to
increase. The b