ged with fine matter in a state of mechanical
suspension. The light from the bottom may sometimes come into play,
but it is not necessary. A storm can render the water muddy, by
rendering the particles too numerous and gross. Such a case occurred
towards the close of my visit to Niagara. There had been rain and
storm in the upper lake-regions, and the quantity of suspended matter
brought down quite extinguished the fascinating green of the
Horseshoe.

Nothing can be more superb than the green of the Atlantic waves, when
the circumstances are favourable to the exhibition of the colour. As
long as a wave remains unbroken no colour appears; but when the foam
just doubles over the crest, like an Alpine snow-cornice, under the
cornice we often see a display of the most exquisite green. It is
metallic in its brilliancy. But the foam is necessary to its
production. The foam is first illuminated, and it scatters the light
in all directions; the light which passes through the higher portion
of the wave alone reaches the eye, and gives to that portion its
matchless colour. The folding of the wave, producing as it does, a
series of longitudinal protuberances and furrows which act like
cylindrical lenses, introduces variations in the intensity of the
light, and materially enhances its beauty.

*****

We have now to consider the genesis and proximate destiny of the Falls
of Niagara. We may open our way to this subject by a few preliminary
remarks upon erosion. Time and intensity are the main factors of
geologic change, and they are in a certain sense convertible. A
feeble force acting through long periods, and an intense force acting
through short ones, may produce approximately the same results. To
Dr. Hooker I have been indebted for some specimens of stones, the
first examples of which were picked up by Mr. Hackworth on the shores
of Lyell's Bay, near Wellington, in New Zealand. They were described
by Mr. Travers in the 'Transactions of the New Zealand Institute.'
Unacquainted with their origin, you would certainly ascribe their
forms to human workmanship. They resemble knives and spear-heads,
being apparently chiselled off into facets, with as much attention to
symmetry as if a tool, guided by human intelligence, had passed over
them. But no human instrument has been brought to bear upon these
stones. They have been wrought into their present shape by the
wind-blown sand of Lyell's Bay. Two winds are, domina