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jungle. Herds of antelope- and horse-like forms (anoplotheres and hippotheres) scattered over the uplands; carnivora (hyaenodon and cynodon) lurking among the rocks and bushes by the water-springs; elephants, tapirs, and warthogs (mastadons, palaeotheres, and hyopotami) down by the river-side; and huge amphibia (halitheres, dinotheres, and crocodiles) lazily sunning themselves on the islets and mudbanks of the far-spreading delta! Plain, lake, estuary, and sea, teeming alike with life during the warmer eocene; abounding in milder forms during the still genial miocene; and gradually assuming more temperate aspects as the pliocene approached more nearly to the ordainings of the current epoch. Such were the leading aspects of the Tertiary Times—times enjoying the genial surroundings of a peculiar geographical distribution of sea and land, and only brought to a close by new terraqueous arrangements inimical (over the greater portion of the northern hemisphere at least) to vegetable and animal luxuriance.'

As Economic Eepositories, the tertiary formations, though greatly inferior to some of the older systems, are not without their local importance. Brick and pottery clays, sands for glass-making, fuller's earth, tripoli or polishing-stone,* gypsum or plaster-of-Paris stone, limestones, burrh for millstones, and a great variety of lignites or brown-coals

* These polishing, infusorial, or microphytal earths are among the most wonderful of tertiary and recent accumulations, alike from their origin and the vast thickness to which they sometimes attain. According to Professor Dana, the infusorial earth of Virginia is in some places 30 feet thick, extends from Herring Bay in the Chesapeake, Maryland, to Petersburg, Virginia, or beyond, and is throughout an accumulation of the silicious remains of microscopic organisms, mostly Diatoms. A still thicker bed, exceeding 50 feet, exists, according to Mr W. P. Blake, on the Pacific at Monterey, and is white and porous like chalk. The "polishing powder" of Tripoli and Bilin, and the " mountain meal" of Tuscany, Sweden, and other countries, are kindred accumulations.

with their associated gums and amber,* are among their most prevalent and valuable products. These lignites, indeed, are year after year being discovered in new areas, and are rapidly rising in economic value, as the only fuel in many localities either for household or for manufacturing purposes. Germany, Italy, Austria, Hungary, Farther India, JTew Zealand, Vancouver Island, the Northern Prairies of America, and other regions, are each possessed of their brown-coals, which will be more and more sought after, and more and more valued, as manufactures, railways, steamboats, and kindred modern appliances extend their influence and demand the cheapest and readiest supply. Compared with the older coals, many of the tertiary lignites are no doubt inferior; but as the demand increases better methods of consumption will be invented, and many of the objections obviated which now stand in the way of their being more largely raised both for domestic and manufacturing purposes. There is thus no formation, however old or however recent, that is not invested with industrial as well as with scientific interest—all that is requisite being research to determine the nature of their products, and skill sufficient to procure and apply them.

* In some of the later lignites, like those of Northern Germany and Burmah, amber and other fossil gums and resins are found in all but their original attachment to the trees from which they were exuded. And in these ambers the insects of the tertiary forests are often as perfectly preserved as the specimens in the cabinet of the most fastidious collector.



There is no substance in nature so protean in form, so incessant in circulation, or so multifarious in' its functions as water. Now aeriform, now liquid, now solid; now in the ocean, now in the atmosphere, now percolating the earth's crust, now coursing its surface and hurrying again to the ocean; now supplying the wants of plants and animals, now wearing down the earth in one part, now accumulating new material in another, and anon locked up, as water of crystallisation, in the mineral structure of the globe for ages. The sum of its existence is change; the whole course of its history a series of marvels. It is, however, only with one feature of its existence, and with a small portion of its history, that we have to do in the present instance • though we have necessarily to glance at its general deportment under heat, the incessant modifier of its form, and the great propeller of its circulation.

At ordinary temperatures, as every one knows, water appears in the liquid state; at high temperatures it passes rapidly into the vaporiform condition, and at low temperatures it becomes solid and crystalline. At 39° Fahr., or thereabouts, it appears to be at its maximum density; at that temperature and above it, under favourable conditions of the atmosphere, it is incessantly passing off as invisible vapour, and diffusing itself through the air; and at 212°, under the usual sea-level pressure of the atmosphere, it boils, and is rapidly converted into steam. From 39° down to 32°, it appears to suffer little change in density; but at and under 32° for fresh water, and 28|° for salt, it is suddenly converted into the crystalline or solid state, and is then known as ice. In this state it has expanded, become lighter, and necessarily floats on its own liquid surface. Ice, then, in ordinary language, is solid or frozen water. From its crystalline structure it occupies more space than when in a liquid state; hence its lightness and flotation, which are further increased by the number of air-cells which are always less or more entangled in its mass.* Compared with water at 60°, whose specific gravity is 1, ice is found to be only .912; hence it floats with about one-ninth of its mass above water, and the remaining portion below. Being formed at 32°, ice may be said to be then in its normal condition; but at lower temperatures it slightly contracts, as was long ago proved by experiments on the ice of the Neva at St Petersburg. t It is therefore clear, that when a bottle or pipe, or close vessel containing water, or a plant

* It is only from water that has been subjected to boiling that ice free from these air-cells can be obtained.

+ In further proof of this contraction, we may cite Sir James Ross, who says :—"We have often in the arctic regions witnessed the astonishing effects of a sudden change of temperature during the winter season upon the ice of the fresh-water lakes. A fall of thirty or forty degrees of the thermometer immediately occasions large cracks, traversing the whole extent of the lake in every direction; some of the cracks opening in places several inches by the contraction of the upper surface in contact with the extreme cold air of the atmosphere." It is also partly by this contractile force that the ice-barriers and ice-walls of the polar seas are broken into floes and fragments.

full of sap, does not burst as soon as the water or sap freezes, it will not do so at all, because as the frost increases in intensity, the ice shrinks more than any other body. It is this ice, its various aspects and functions, that forms the subject of the present Sketch; its geological operations being those, of course, to which the attention of the reader will be more especially directed.

In treating of Ice in a popular way it may be conveniently arranged under three great categories—ice in the atmosphere; ice on land; and ice on water. The ice or frozen water in the atmosphere is the great nursing parent of the ice on land; and the ice accumulated on the land becomes in the long-run one of the most remarkable features of the ice that floats on the water. As the vapour that ascends from the ocean is condensed and falls as rain on the land, and this rain finds its way again by runnel and river to the sea; so the vapour frozen in the air descends on the land, where, accumulating for ages, it slowly grinds and pushes its way once more to the ocean. In this way all the forms of ice are inseparably connected in one great and incessant round of circulation, and we only separate them provisionally for the purpose of intelligible description. First, then, as regards the ice in the atmosphere, the most casual observer must have noted the frequent formation of hoar-frost, snow, and hail. The rapid radiation of heat from the earth's surface, by which the invisible vapour of the atmosphere is converted into dew, has only to be carried beyond the limit of 32°, when hoar-frost is produced, crisping the herbage, or floating, in still conditions of the air, in clouds of crystalline spicules. A more rapid condensation of rain or vapour produces hail, which may occur at all seasons, and under every latitude, and may fall in soft snowy drops, or pellets of ice, from the size of a coriander

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