main united might render the bodies more easily fusible. This opinion was subsequently confirmed by an experiment of Sir James Hall, who found that limestone, which is infusible when exposed to heat in the atmosphere, could be melted when the carbonic acid was retained in union with it by pressure. Dr Hutton's third fact was, that the stratified rocks, which must originally have been formed either horizontal or nearly so, are now elevated at all angles, and some even perpendicular. Though evidently formed at the bottom of the sea, many of them are now raised ten or fifteen thousand feet above its surface. From this, as well as from the inflexions, the breaking and separation of the strata, it is inferred that they have been elevated by some expansive force below, similar to the cause of earthquakes or volcanoes. Hence it is probable that the internal heat which consolidated, has also elevated and disturbed the strata. Among these marks of disturbance, veins, or great fissures in the rocks filled with materials different from the sides, are the most conspicuous, and form the fourth great fact on which this theory depends. These comprise not only metallic veins but dykes of trap, porphyry, and granite-all crystalline substances, containing no remains of organized bodies. From their appearance Dr Hutton concluded that they were of later origin than the rocks they intersect; that their materials had been melted by subterraneous heat, and violently injected among the fissures of these rocks. This mode of origin he ascribed to all the masses of trap, porphyry, granite, or other unstratified rocks, found among the strata. The fifth fact to which he directed attention completes the great circle of natural changes. All mineral bodies, when raised into the atmosphere, are without exception found going to decay; from the shore of the sea to the top of the mountain, from the softest clay to the hardest quartz, all are wasting. But the materials thus formed are carried down by rivers and deposited in the ocean. Here, however, as the first fact noticed shows, they do not remain, but are consolidated and raised up in new beds, forming new continents. How often these vicissitudes have been repeated nothing in nature gives us any means to discover; there are remains in mineral bodies that lead us back to continents from which the present are the third in succession, but how many more there may have been we cannot tell. Hence, in the mineral kingdom, as in the animal and vegetable world, and in the planetary system, there is a series of revolutions of which we see neither the beginning nor the end, no mark either of the commencement or termination of the present order. As Playfair eloquently observes, 'It is unreasonable, indeed, to suppose that such marks should anywhere exist. The Author of nature has not given laws to the universe, which, like the institutions of men, carry in themselves the elements of their own destruction; he has not permitted in his works any symptom of infancy or of old age, or any sign by which we may estimate either their future or their past duration. He may put an end, as he no doubt gave a beginning, to the present system, at some determinate period of time; but we may rest assured, that this great catastrophe will not be brought about by the laws now existing, and that it is not indicated by anything which we perceive.'

Such is the simple yet comprehensive system of Hutton, which, in most of its parts, is now generally adopted. He has been blamed for hasty generalization, but wrongly, as the facts he had observed fully warranted all the conclusions he deduced from them. In his own time the more formidable charge of impiety was brought against him; and because he would not attempt to explain the nature of creation, he was alleged to deny it altogether. No charge could have less foundation in the character of his work, in which he ever shows a laudable anxiety to point out the marks of wisdom, design, and goodness, observable in the structure of the universe. The high antiquity he was compelled to ascribe to the earth, was also treated as an attack on the truth of Scripture, but is now generally admitted to be no less consistent with the words of Moses, properly interpreted, than absolutely required

by the facts of nature. It is very remarkable that all the numerous additions to geology since his time, have done little more than fill up the subordinate parts of the picture, without altering any of its great lineaments. Even the numerous discoveries in organic remains are only carrying the principles he had established, in reference to the mineral structure of the earth, into the animal and vegetable kingdoms, and showing that they too are subject to revolutions, and that their genera and species have repeatedly changed along with the continents or oceans they inhabited.

The natural history of the earth was not the only branch of physical science in which Hutton is entitled to rank as a great discoverer. Meteorology, or the laws that regulate the atmosphere, also engaged his attention; and his theory of rain was one of the first steps to a scientific knowledge of this subject. Philosophers had long been puzzled to account for this very common phenomenon. It was well known that as the temperature of any mass of air increases, it becomes capable of dissolving a greater quantity of moisture. Now Dr Hutton saw that if the increase of moisture in the atmosphere was in the same or in a less ratio with the increase of heat, a mixture of two portions of air at different temperatures, each loaded with its full amount of humidity, would produce no condensation of moisture, and consequently no rain. But every day experience proves that such a condensation takes place, when warm and moist air, like the breath, is mixed with colder air; and hence a different law must prevail, and the moisture must increase more rapidly than the temperature. Hence, where currents of air, or winds of different temperature, meet and mix in the atmosphere, a deposition of moisture must take place, forming clouds, or, if the supply of humidity be sufficient, rain. By this simple theory all the aqueous meteors of the atmosphere may be explained; and Dr Hutton confirmed its reality by showing that the rain in different regions of the earth was proportional to the humidity of the atmosphere over them. He also pointed out the reason why, in level countries far from the sea, like the great Sahara, no rain falls, condemning them to perpetual sterility; whereas when a mountain tract occurs, causing the various currents of air to mingle, rain is common, perennial springs abound, and isles of verdure, like Fezzan or Palmyra, burst forth in the wilderness.

This theory, though it met with some opposition at first, is now generally received. It was not his only contribution to this science, for observing that evaporation proceeded in a vacuum, he anticipated the discovery of Dalton, that the air has no chemical action on the vapour contained in it. He also explained the diminution of temperature es we ascend in the atmosphere, by the expansion of the air, causing a portion of its heat to become latent. His theories being now before the public, he made excursions into various parts of Scotland in order to compare certain parts of them with actual observation. The occurrence of granite veins in the strata was then little known, and he sought some place where his theory on this subject might be confronted with nature. The line where the granite kernel of the Grampians unites with the slaty mountains on the south, was likely to offer such points; and an invitation from the Duke of Athol to accompany him to Glentilt, in 1785, gave him an opportunity of looking for them. Here, in less than a mile, he found six large veins of red granite traversing the black mica-slate, and expressed his feelings of delight at this testimony of nature to the truth of his system so strongly, that the guides who accompanied him were convinced that nothing less than the discovery of a vein of silver or gold could call forth such marks of joy and exultation. In the following summer, he observed similar veins in Galloway; and in 1787, also in Arran, from which he returned highly gratified, having, as he was wont to say, no where found his expectations so much exceeded as in the grand and instructive appearances with which nature has adorned this little island. In it he also saw the secondary rocks resting unconformably on those of pri

isted; while a number suppose that species, for the most part, must have originated where they now appear as the natural and untransported products of the soil and climate. Some again have conjectured that genera only, or leading families of plants, were at first created, and that the species sprung from these. It seems pretty evident, too, that since the first creation of plants the earth's surface has suffered many changes and modifications, by which both the relative position of land and sea, and the relative states of temperature, have also undergone fluctuations; so that, from these causes, the original distribution of plants must have also been greatly modified. It is sufficient for us, however, to know that at the present day certain zones or belts of vegetation exist on the earth's surface that the allocation of these zones is influenced in a considerable degree, though not entirely, by temperature-and that, notwithstanding this allocation to particular localities, there is still a great tendency in plants to scatter their species by natural agencies; while man, by his art, is continually at work in transplanting them from one climate to another, and successfully cultivating those that most tend to his comfort and happiness. The different kinds of corn, the grape, the sugar-cane, the bread-fruit, the potato, the coffee plant, and innumerable others, have thus been extensively spread over the earth.

Altitude has also an effect on temperature, and on the localization of plants. As elevated situations are colder than those on a level with the ocean, the higher we ascend mountains the lower the temperature becomes, till at last we reach their summits tipt with snow; and thus we experience a change of climate corresponding to that observed in passing from the equator to the poles. A similar change of vegetation is also visible. Thus in ascending the Alps or Pyrenees, we find the oaks and vines, characteristic of a temperate climate, around their base. A little higher these have disappeared, but pines, birches, and alders are found. Still higher, the absence of trees, while there yet appear small willows and heaths, with many mosses and saxifrages, recalls the treeless flora of the arctic regions. Many of the plants found high on the mountains of Southern Europe are indeed specifically the same as those of Spitzbergen and Greenland. Below these we have Lapland species; lower still, those of Britain. Nearly one half of the plants of Spitzbergen are found on the hills of Scotland; those of England, lower in height, have only one fourth. The height at which perpetual snow lies on the mountains of the equator is about 16,000 feet, becoming lower as we advance to the poles, and resting on the sea level in seventy or eighty degrees of north latitude. At these points vegetation of course ceases, unless we except that curious red lichen which vegetates even on the surface of snow, and has been called red-snow (palmella nivalis). Beyond the arctic circle the number of plants is extremely limited. Captain Ross, speaking of a tribe of Esquimaux that he met with on the shores of Baffin's Bay, says Their knowledge of wood seemed to be limited to some plant like heath, of a dwarfish growth, with stems no thicker than the finger. They knew not what to think of the timber they saw on board the ship; and so little notion had they of cloth or any kind of vegetable texture, that, when presented with a shirt, they inquired of what animal's skin it was made.' In Norway and Lapland, the trees which are found to approach nearest the limits of perpetual snow are the dwarf birch and the dwarf willow, if they can be properly denominated trees; for the birch seldom exceeds two or three feet in height, and the willow is even smaller-so small, indeed, that half a dozen fullgrown plants, with their roots, stems, branches, and leaves complete, may be laid out on the fourth of a sheet of common letter-paper. Next to these diminutive trees succeed the birch, the mountain-ash, the willow, the Scotch fir, the larch, and the pine. Forests of these trees, growing to a great height, cover the northern parts of Europe, and extend from Russia into the northern regions of Asia. As we approach a little farther south, the oak, the beech, and the elm make their appearance. These trees flourish in full luxuriance in Britain, and clothe the mountain

sides of the whole of Southern Europe. In these temperate regions, too, wheat and the other grains, as well as the grasses, attain their greatest perfection; and here also is the proper region of the grape, apple, pear, plum, apricot, almond, chestnut, currant, gooseberry, strawberry, and many similar fruits. According to Humboldt, the cultivation of the vine succeeds only in those climates where the medium temperature of the year is between fifty and sixty-eight degrees, and where especially the summer heat is not less than sixty-eight to seventy. In the old world, this temperature is found to prevail as far north as the fiftieth degree of latitude, whereas, in the new world, it does not extend beyond the fortieth. It is to the west of Milan, in Italy, that the cultivation of rice first begins to make its appearance. This is truly a tropical grain, and forms a valuable substitute for the wheat and barley of more temperate climes. The rice plant is a species of grass bearded like barley; it grows in marshy places, and hence, for its successful culture, the land must be irrigated with water at two different periods during its growth and maturation. The olive, too, is extensively cultivated in the south of Europe, as well as throughout the more temperate parts of Asia; and the orange and lemon trees fill the air with the fragrant odours of their blossoms.

In Italy, and on both sides of the Mediterranean, the American aloe blooms in the open air, and one species of palm, the dwarf palm, here first makes its appearance. The myrtle, laurel, geranium, and many of our choice garden flowers, here grow in the fields and hedges, without the culture or the care of man. From the same countries, we originally derived the hyacinth, the tulip, the iris, the ranunculus, which appear to have been imported during the reign of Elizabeth. To this list may be added the horse-chestnut, the lilac, the sweet jasmin, the melon, and the cucumber. That the melon and cucumber were raised in Egypt at a very remote period, appears from the complaints of the Israelites when they murmured against Moses and Aaron in the wilderness. 'We remember the fish,' said they, 'which we did eat in Egypt freely; the cucumbers, and the melons, and the leeks, and the onions, and the garlic. Wherefore have ye made us to come up out of Egypt to bring us into this evil place? It is no place of seed, or of figs, or of vines, or of pomegranates; neither is there any water to drink.' But it is in the torrid zone that vegetation assumes its most luxuriant forms. 'When a traveller newly arrived from Europe penetrates for the first time into the forests of South America, if he is strongly susceptible of the beauty of picturesque scenery, he can scarcely,' says Humboldt, define the various emotions which crowd upon his mind; he can scarcely distinguish what most excites his admiration—the deep silence of these solitudes— the individual beauty and contrast of forms—or that vigour and freshness of vegetable life which characterizes the climate of the tropics. It might be said, that the earth, overloaded with plants, does not allow them space to unfold themselves. Not only the ground, but the trunks and branches of trees, are covered and loaded with flowers of all hues; creeping plants often reach from the ground to the very summits of the trees, and pass from one to the other at the height of a hundred feet, so as to deceive the observer, and lead him to confound the flowers, the fruit, and the leaves which belong to different species. So thick and uninterrupted are the forests which cover the plains of South America, between the Orinoco and the Amazon, that, were it not for intervening rivers, the monkeys, almost the sole inhabitants of these regions, might pass along the tops of the trees for several hundred miles together, without touching the earth!'

Yet the medium heat of the equatorial regions is by no means so different from that of other parts of the globe as we might be led to suppose, by observing the extraordinary extent of tropical vegetation. In a climate where the bamboo attains in a few months the height of sixty feet, and palms and other plants shoot up with surprising rapidity, we should be inclined to look for a correspond

ing increase of the sun's rays. This, however, is not the case. In general, the mean temperature of the equator does not exceed eighty-two degrees; a heat by no means uncommon in our English summers. It is true, this heat is more steady, is not interrupted by great night chills, and is accompanied by moisture; and what perhaps also contributes to the vigour of vegetation, an abundant evolution of electricity.

grows to two hundred and twenty feet in height, with a considerable breadth of trunk, forming, on the whole, one of the most magnificent objects in nature.

Fortunately, those plants which are most useful to man are those which are best suited by their natures to bear the extremes of climate, and which are capable of being raised in all ordinary soils. This is the case with the various kinds of corn-the potato, the turnip, the carrot, and many other vegetables. It is the same with all our most useful timber and fruit trees. The industry of man has done much to transport and cherish the useful plants of various climates, and to inure them to new soils. But besides this, his art and enterprise enables him to transport the produce of one soil to another, and thus to diffuse the necessaries of life over every region of the globe. The astonishing progress of steam navigation has now, we may say, brought the tropical regions within eight or ten days' journey of us. A hundred years ago, it was as great an effort, and took nearly as long time, for a market gardener, in the midland counties of England, to bring up the produce of his garden to the London market, as it now does for a West India steamer to transport the produce of those fruitful isles across the Atlantic. It was but the other week that the London market was supplied with a cargo of fresh pineapples brought in ten days from Barbadoes. We may now, in the depth of our winter, be supplied with all the rich concocted juices of more favoured climes, where the sun never ceases to exercise a genial and a summer in

our forest trees.

But it is chiefly the palm tribe that imparts a peculiarity to the aspect of tropical countries. Of this family, there are upwards of one hundred and thirty different kinds. This tree differs from others in rising up to a considerable height in one single stem; the large broad leaves then spring out from the summit, and the fruit grows in the centre of this bunch of foliage. Not only do these excel every other family of plants in beauty and stateliness, but also in the great abundance of their fruits. Amidst the solitudes of the South American forests, in plains far remote from human habitation, Humboldt found the ground covered with the fruit of these trees, in places to the depth of three inches. More than twelve thousand flowers have been counted in a single swathe of the date palm. These palms, especially the cocoa, afford food, oil, cordage, and wood, for every useful purpose. The cabbage palm, the wax palm, the banana, and date, all furnish substances highly useful to man.

In India and its islands, the greater number of the spices are produced, as cinnamon, cloves, camphor, ginger, pepper, nutmeg, as well as gums, resins, and medicinal substances. China produces tea. The West Indies sugar, coffee, pine apples. America pours forth its cotton, mahogany, and various dye-woods. From Peru we derived the inestimable potato; and Mexico has furnished some of our most splendid garden plants, as the dahlia and sun-flower. One of the most singular of flowers, the Rafflesia Arnoldii grows in Sumatra. The blossom bursts from out the warm fertile earth, and when fully expanded, measures at least three feet in diameter. It consists of five large thick spotted petals, with a central disc-its odour is foetid, and resembles that of decaying mushrooms. The largest tree in the world grows in Senegal; it is the famous Baobab tree of Adanson. Its huge trunk, twelve feet from the ground, measures thirty feet across; its height is seventy feet, and the canopy formed by its numerous branches and matted leaves will contain under it many troops of elephants and soldiers. Though the largest, this is not the highest of trees. Many of the palms attain a height of one hundred and fifty feet; and a species of pine tree of Australia, the araucaria excelsa,

THE SKELETON'S CAVE.

AN AMERICAN STORY.

ONE pleasant summer morning a party of three persons set out from a French settlement in the western region of the United States, to visit a remarkable cavern in its vicinity. They had already proceeded for the distance of about three miles through the tall original forest, along a path so rarely trodden that it required all their attention to keep the track. They now perceived through the trees the sunshine at a distance, and as they drew nearer they saw that it came down into a kind of natural opening at the foot of a steep precipice. At every step the vast wall seemed to rise higher and higher; its seams, and fissures, and inequalities, became more and more distinct; and far up, nearly midway from the bottom, appeared a dark opening, under an impending crag. The precipice seemed between two and three hundred feet in height, and quite perpendicular. At its base, the earth for several rods around was heaped with loose fragments of rock, which had evidently been detached from the principal mass, and shivered to pieces in the fall. A few trees, among which were the black walnut and the slippery elm, and here and there an oak, grew scattered among the rocks, and attested by their dwarfish stature the ungrateful soil in which they had taken root. But the wild grape vines which trailed along the ground, and sent out their branches to overrun the trees around them, showed by their immense size how much they delighted in the warmth of the rocks and the sunshine. The celastrus also here and there had wound its strong rings round and round the trunks and the boughs till they died in its embrace, and then clothed the leafless branches in a thick drapery of its own foliage. Into this open space the party at length emerged from the forest.

'Yonder is the Skeleton's Cave,' said one of them, who stood a little in front of the rest. As he spoke he raised his arm, and pointed to the dark opening in the precipice already mentioned.

The speaker was an aged man, of spare figure, and Whoever a mild, subdued expression of countenance. looked at his thin grey hairs, his stooping form, and the emaciated hand which he extended, might have taken him for one who had passed the Scripture limit of threescore years and ten; but a glance at his clear and bright hazel eye would have induced the observer to set him