Viewed simply in its picturesque aspect, this _olive leaf_ of the Old Red seems not at all devoid of poetry. We sail upwards into the high geologic zones, passing from ancient to still more ancient scenes of being; and, as we voyage along, find ever in the surrounding prospect, as in the existing scene from which we set out, a graceful intermixture of land and water, continent, river, and sea. We first coast along the land of the Tertiary, inhabited by the strange quadrupeds of Cuvier, and waving with the reeds and palms of the Paris Basin; the land of the Wealden, with its gigantic iguanodon rustling amid its tree ferns and its cycadeæ, comes next; then comes the green land of the Oolite, with its little pouched insectivorous quadruped, its flying reptiles, its vast jungles of the Brora equisetum, and its forests of the Helmsdale pine; and then, dimly as through a haze, we mark, as we speed on, the thinly scattered islands of the New Red Sandstone, and pick up in our course a large floating leaf, veined like that of a cabbage, which not a little puzzles the botanists of the expedition. And now we near the vast Carboniferous continent, and see along the undulating outline, between us and the sky, the strange forms of a vegetation, compared with which that of every previously seen land seems stunted and poor. We speed day after day along endless forests, in which gigantic club-mosses wave in air a hundred feet over head, and skirt interminable marshes, in which thickets of reeds overtop the mast-head. And, where mighty rivers come rolling to the sea, we mark, through the long-retiring vistas which they open into the interior, the higher grounds of the country covered with coniferous trees, and see doddered trunks of vast size, like those of Granton and Craigleith, reclining under the banks in deep muddy reaches, with their decaying tops turned adown the current. At length the furthermost promontory of this long range of coast comes full in view: we near it,—we have come up abreast of it: we see the shells of the Mountain Limestone glittering white along its further shore, and the green depths under our keel lightened by the flush of innumerable corals; and then, bidding farewell to the land forever,—for so the geologists of but five years ago would have advised,—we launch into the unmeasured ocean of the Old Red, with its three consecutive zones of animal life. Not a single patch of land more do those geologic charts exhibit which we still regard as new. The zones of the Silurian and Cambrian succeed the zones of the Old Red; and, darkly fringed by an obscure bank of cloud ranged along the last zone in the series, a night that never dissipates settles down upon the deep. Our voyage, like that of the old fabulous navigators of five centuries ago, terminates on the sea in a thick darkness, beyond which there lies no shore and there dawns no light. And it is in the middle of this vast ocean, just where the last zone of the Old Red leans against