ndeed, the spray sometimes
rises without solution of continuity to the region of clouds, becoming
gradually more attenuated, and passing finally through the condition
of true cloud into invisible vapour, which is sometimes reprecipitated
higher up. All the phenomena point distinctly to the centre of the
river as the place of greatest mechanical energy, and from the centre
the vigour of the fall gradually dies away towards the sides. The
Horseshoe form, with the concavity facing downwards, is an obvious and
necessary consequence of this action. Right along the middle of the
river the apex of the curve pushes its way backwards, cutting along
the centre a deep and comparatively narrow groove, and draining the
sides as it passes them. [Footnote: In the discourse the excavation of
the centre and drainage of the sides action was illustrated by a model
devised by my assistant, Mr. John Cottrell.] Hence the remarkable
discrepancy between the widths of the Niagara above and below the
Horseshoe. All along its course, from Lewiston Heights to its present
position, the form of the fall was probably that of a horseshoe; for
this is merely the expression of the greater depth, and consequently
greater excavating power, of the centre of the river. The gorge,
moreover, varies in width, as the depth of the centre of the ancient
river varied, being narrowest where that depth was greatest.

The vast comparative erosive energy of the Horseshoe Fall comes
strikingly into view when it and the American Fall are compared
together. The American branch of the river is cut at a right angle by
the gorge of the Niagara. Here the Horseshoe Fall was the real
excavator. It cut the rock, and formed the precipice, over which the
American Fall tumbles. But since its formation, the erosive action of
the American Fall has been almost nil, while the Horseshoe has cut its
way for 600 yards across the end of Goat Island, and is now doubling
back to excavate its channel parallel to the length of the island.
This point, which impressed me forcibly, has not, I have just learned,
escaped the acute observation of Professor Ramsay. [Footnote: His
words are: 'Where the body of water is small in the American Fall, the
edge has only receded a few yards (where most eroded) during the time
that the Canadian Fall has receded from the north corner of Goat
Island to the innermost curve of the Horseshoe Fall.'--Quarterly
Journal of Geological Society, May 1859.] T