To this purity Niagara owes its exquisite variety of colour. To find the blues we must look, of course, above Goat Island, where the sky is reflected in smooth if quickly flowing currents. But every other tint and tone that water can take is visible in or near the Falls themselves. In the quieter parts of the gorge we find a very dark, strong green, while in its rapids all shades of green and grey and white are blended. The shallower rapids above the Falls are less strongly coloured, a beautiful light green predominating between the pale-grey swirls and the snowy crests of foam--semi-opaque, like the stone called aquamarine, because infused with countless air-bubbles, yet deliciously fresh and bright. The tense, smooth slant of water at the margin of the American fall is not deep enough to be green. In the sunshine it is a clear amber, and when shadowed, a brown that is darker, yet just as pure. But wherever the Canadian fall is visible its green crest is conspicuous. Far down-stream, nearly two miles away, where the railroad-bridge crosses the gorge, it shows like a little emerald strung on a narrow band of pearl. Its colour is not quite like that of an emerald, although the term must be used because no other is more accurate. It is a purer colour, and cooler, with less of yellow in it--more pure, more cool, and at the same time more brilliant than any colour that sea-water takes even in a breaking wave, or that man has produced in any substance whatsoever. At this place, we are told, the current must be twenty feet deep; and its colour is so intense and so clear because, while the light is reflected from its curving surface, it also filters through so great a mass of absolutely limpid water. It always quivers, this bright-green stretch, yet somehow it always seems as solid as stone, smoothly polished for the most part, but, when a low sun strikes across it, a little roughened, fretted. That this is water and that the thinnest smoke above it is water also, who can believe? In other places at Niagara we ask the same question again.