Not only has the Glacial epoch left these organic traces of its existence, however; in some parts of New Hampshire, where the glaciers were unusually thick and deep, fragments of the primaeval ice itself still remain on the spots where they were originally stranded. Among the shady glens of the white mountains there occur here and there great masses of ancient ice, the unmelted remnant of primaeval glaciers; and one of these is so large that an artificial cave has been cleverly excavated in it, as an attraction for tourists, by the canny Yankee proprietor. Elsewhere the old ice-blocks are buried under the _debris_ of moraine-stuff and alluvium, and are only accidentally discovered by the sinking of what are locally known as ice-wells. No existing conditions can account for the formation of such solid rocks of ice at such a depth in the soil. They are essentially glacier-like in origin and character: they result from the pressure of snow into a crystalline mass in a mountain valley: and they must have remained there unmelted ever since the close of the Glacial epoch, which, by Dr. Croll's calculations, must most probably have ceased to plague our earth some eighty thousand years ago. Modern America, however, has no respect for antiquity: and it is at present engaged in using up this palaeocrystic deposit--this belated storehouse of prehistoric ice--in the manufacture of gin slings and brandy cocktails. As one scales a mountain of moderate height--say seven or eight thousand feet--in a temperate climate, one is sure to be struck by the gradual diminution as one goes in the size of the trees, till at last they tail off into mere shrubs and bushes. This diminution--an old commonplace of tourists--is a marked characteristic of mountain plants, and it depends, of course, in the main upon the effect of cold, and of the wind in winter. Cold, however, is by far the more potent factor of the two, though it is the least often insisted upon: and this can be seen in a moment by anyone who remembers that trees shade off in just the self-same manner near the southern limit of permanent snow in the Arctic regions. And the way the cold acts is simply this: it nips off the young buds in spring in exposed situations, as the chilly sea-breeze does with coast plants, which, as we commonly but incorrectly say, are "blown sideways" from seaward.