These results are valuable in the light of general approximations, but they are not to be regarded as rigidly applying to all places in the respective latitudes stated. The elevation of the snow-line under the same parallel exhibits irregularities which are the effect of local circumstances. Thus there are plains on the Himalaya mountains 15,000 feet above the level of the sea, which produce fine pasturage; and barley and buck-wheat flourish at the height of 11,000 feet, which is above the region of perpetual snow on the Andes, in the same latitude. The southern declivity of the Himalaya, also, has the snow-line at an elevation of about 13,000 feet; but instead of descending as we proceed farther north, it rises to the height of 16,000 feet. This is clearly an irregularity

referable to the fact that the south side of the range ascends abruptly from the low level plains of Bengal, while the north side descends into a plain which is itself immensely elevated, and a higher temperature is produced there, elevating the snow-line by the reflection of the solar action from the large and contiguous masses of land. The Pyrenees, likewise, and the Caucasus, under the same parallel of latitude, exhibit a great discrepancy. Though the general climate of the adjacent country is warmer in the case of the Pyrenees, yet the snow-line on Mont Perdu, according to Raymond, is found at the height of 8700 feet, while on Elbürz it occurred at the elevation of 10,880 feet, as observed by Englehardt and Dr. Parrot. South of Elbürz, by only 3° of latitude,

Parrot found the snow-line on Ararat at 14,080 feet, which is 5000 feet above its elevation, under the parallel of 40°, as registered in the table.

The Russian traveller, Parrot, justly remarks that the time of the year when the snow limits are observed should be particularly noted, in order to be capable of being determined with tolerable precision. "On that point it may be laid down, in general, that it is only in the end of autumn, before winter has brought much new snow, and when the heat of autumn shall have melted as much as it can of the old, that such observations can lead to a correct result. For mountains such as Ararat, Caucasus, the Alps, the Pyrenees, and, in general, all mountains in middle latitudes, August and September are the only months which can be used for determining the true limits of perpetual snow, because, during these months, although the great heat is for the most part gone by, yet large masses of snow still go on melting away, till the actual setting in of winter in these regions puts a stop to the process." The difference observed in the elevation of the curve of congelation between places under the same parallel of latitude may, in several cases, have been owing to the observations being made at different times of the year. He thus accounts for the height of the snow-line in the instance of Ararat:

"In the country around there reigns an extraordinary degree of heat, the rays of the mid-day sun striking directly on the south side of the mountain, while on its northern side the valley of the Araxes preserves to a late season of the year the heat received from the slopes of the Gorkchai mountains. In July and August the people fly from the sultriness of the plain-a sultriness which did not allow me, in the latter half of October, to make any exertions out of doors in my usual clothing. At the end of that month the thermometer still stood at 68° Fahr. This excessively hot air continually ascends during the summer up the sides of Ararat, warming its soil, and encroaching uninterruptedly on its snows. In this way alone can I explain the great heat which allowed me, in the latter end of September (old style), to spend two nights on bare rocks in the open air, without a pelisse, and at the height of 13,800 feet above the sea. If to the circumstance of the warm streams of air rushing up the sides of Ararat the greater part of the year we add the isolated position of that mountain, the icy head of which is the only one in a very wide tract that rises to a great height above the surrounding country, and which is, therefore, of course, less able to resist the influx of warmth from below, than a more widely extended mass of snow, such, for example, as occurs in the Alps, we can explain satisfactorily enough the extraordinary height of the snow limits on Ararat, which, according to my observations, are 14,080 feet above the level of the sea."

From this effect of elevation upon temperature it is obvious that a country may have all the varieties of climate within a very scanty area; and accordingly, in several parts of the torrid zone, an unfortunate geographical position is compensated by a happy physical contour. The low coasts of Mexico, and the elevated table-land 9000 feet above the sea, with its ridge of lofty peaks, of which Popocatapetl and Orizaba rise above the snow-line, exhibit a striking example of a hot climate in close contiguity to one mild and equable, and to another bordering upon arctic rigour. The hot regions, tierras calientes, include the country along the eastern and western shores under the elevation of 2000 feet, where the mean temperature is about 77°, and sugar, indigo, cotton, and bananas flourish luxuriantly. Above these are the temperate regions, tierras templadas, which lie along the slopes of the mountains at an elevation of from 2000 to 5000 feet. Here the yellow fever, the scourge of the low grounds, is unknown; and the mean heat of the year is from 68° to 70°. The traveller enjoys a genial air, and encounters the oaks, cypresses, pines, tree-ferns, and the cultivated cereal plants of Europe. He next arrives at the cold regions, tierras frias, which include the table-lands and the mountains above 5000 feet. On the borders of this zone the climate is still pleasant, but beyond the elevation of 8000 feet it becomes severe, and gradually assumes the character of the polar latitudes.

Switzerland, in a similar manner, exhibits a variety of climates within the area of a few square miles, with the vegetable productions peculiar to each, as the effect of its surface-elevations and irregularities. The Valais, one of the cantons, displays this diversity very remarkably. In that narrow and deep longitudinal valley, the extremes of temperature occur at a trifling distance from each other, the cold of Iceland and the heat of a Sicilian summer; and while in some of its inhabited parts fruit will not ripen, in others the wild asparagus is seen to grow, and the almond, the fig, and the pomegranate attain the greatest perfection. This high temperature arises from its lofty mountain walls preventing the free passage of the air, and reflecting from their sides the heat they receive from the rays of the sun, which impinge upon them more directly than on a level surface; and hence the singular fact has been witnessed, in an elevated valley of Mont Blanc, of the temperature in the centre being so much increased by reflection, that the spot has been covered with flowers and verdure in the midst of perpetual snows and glaciers. Vines grow in the Valais to the height of 2380 feet above the level of the sea;

trees to 6700 feet; shrubs to 8500; a few plants to 10,600, beyond which are a few lichens; and vegetation ceases entirely at the height of 11,000 feet, amid arctic cold. The following is the extreme line of elevation above the sea-level observed here by individual classes of vegetation:

The valley of the Adige extending from near the summit of Mont Brenner in the

4800

- 6600

- 5100

7400

Tyrolese Alps to the Lago di Garda, reposing on the edge of the softer scenes of Italy, exhibits a scale of productions which marks the alteration of climate, in the course of about a hundred miles, the effect of a descent from a high to a low elevation. "We have first," says Inglis speaking of its northern extremity, "Alpine productions; but to pass these over, and to note only the productions of cultivated land,-we have first then, barley, thin and scanty, and a few hardy vegetables. We come next to Indian corn of a poor growth, with barley more vigorous, oats, grass, and firs. The third gradation brings us to a little wheat, mingled with all these, and to some walnut trees, besides fir. In the fourth division of the valley, we find Indian corn and wheat growing luxuriantly, vines beginning to appear, and fruit trees, especially the cherry, in abundance. The fifth gradation shows us, with all these productions, vines in luxuriance, and magnificent walnut trees entirely superseding the hardier wood. At the sixth step we find some additions to these: the mulberry begins to appear, and fruits of the more delicate descriptions are found. The seventh division presents the vine in its perfection, the mulberry in its abundance, and the fruits we have seen before, in greater luxuriance. The eighth and last gradation shows us, with all that we have seen before, the olive, the

pomegranate, and the fig. The valley of the Adige is indeed peculiarly calculated for the display of this scale: the low temperature, which in its upper parts accompanies its great elevation, gives us the productions of a northern latitude; while as we descend, the valley being open to the south, and shut in in every direction, a vegetation is produced that belongs to a more southern latitude than the country enjoys."

Etna exhibits a striking example of variety of climate, that of the valleys at its base being as different from the higher parts, as an equatorial from a polar latitude. The whole mountain is divided into three districts, called La Regione Culta, or the fertile region; La Regione Sylvosa, the woody region; and La Regione Deserta, the barren region. The temperature and productions of these districts are as diverse from each other as those of the three zones of the earth, and, with almost equal propriety, they might be styled, the torrid, the temperate, and the frigid zones. But these zones are again subdivided, the limits of their respective parts being determined by families of plants which require a certain amount of temperature for their growth. Seven distinct botanical regions are noticed upon Etna. The first, or lowest, is confined to the elevation of about a hundred feet above the level of the sea. Here the palm tree is met with, the banana, the Indian fig, and the sugar-cane, with varieties of mimosa and acacia in the gardens, which require a conservatory in the northern parts of Europe. The second region presents cotton, maize, the orange, the lemon, and the shaddock, and most of the plants of southern Spain, France, and Italy. Its limit is about 2000 feet above the level of the sea, where the culture of the vine ceases. The third or woody zone lies between the height of 2000 and 4000 feet. Here the cork-tree flourishes, the oak, the maple, and the chestnut attain a magnificent size, the Castagno dei cento cavalli, or chestnut of a hundred horses, being more than two hundred feet in circumference, as measured by Brydone. It presented five large and distinct trunks, without any appearance of bark in the inside, which sanctions the popular belief of these having been united in one stem. The canon Recupero, an ecclesiastic, was at the expense of carrying up peasants with tools to dig round the tree, and found the trunks proceeding from one root. The fourth region occupies a belt on the mountain between the elevation of 4000 and 6000 feet, and is characterised chiefly by the birch and Scotch fir. The fifth zone, between 6000 and 7500 feet, is sub-alpine, and produces the barberry, soap-wort, and juniper, which are found in the sixth, between 7500 and 9000 feet, in connection with a few plants peculiar to it. The seventh region extends from the preceding two hundred feet higher, which marks the extreme limit of vegetation. It presents only a few lichens, and beyond the height of 9200 feet utter barrenness prevails.

The Island of Teneriffe, with its celebrated Peak rising to the height of 12,176 feet, presents five zones of vegetation, arranged in stages one above another, extending through a perpendicular elevation of 11,190 feet, to which vegetation ascends in that tropical latitude. The region of Vines rises from the level of the sea to a height varying from 1200 to 2000 feet, and exhibits various kinds of arborescent Euphorbiæ, Mesembryanthema, the Cacalia Kleinia, the Dracona, and other plants, whose naked and tortuous trunks, succulent leaves, and bluish-green tints are distinguishing features of African vegetation, The great dragon-tree of Orotava, a species of very slow growth, Humboldt found to be sixty feet high, with a circumference of forty-eight feet near the roots, the trunk separating at a particular point into a variety of branches in the form of a candelabrum. In this zone, the date-tree flourishes, the sugar-cane, the plantain, the Indian fig, the olive, wheat, and the fruit-trees of Europe. The region of Laurels includes the woody part of Teneriffe; and abounding with springs, the ground is never parched with drought, but presents an ever-verdant turf. Four species of laurel, one of oak resembling that of the table-land of Thibet, two of iron-tree, and a variety of evergreen trees of the myrtle