organic life in a zone that is nearly 3000 feet lower than that to which it attains in the equinoctial region of the Cordilleras.

But the countries bordering on the equator possess another pp. 281-326.) My opinion on the difference of height of the snow-line on the two sides of the Himalaya has the high authority of Colebrooke in its favour. He wrote to me in June, 1824, as follows:-"I also find, from the data in my possession, that the elevation of the line of perpetual snow is 13,000 feet. On the southern declivity, and at lat. 31°, Webb's measurements give me 13,500 feet, consequently 500 feet more than the height deduced from Captain Hogdson's observations. Gerard's measurements fully confirm your opinion that the line of snow is higher on the northern than on the southern side " It was not until the present year (1840) that we obtained the complete and collected journal of the brothers Gerard, published under the supervision of Mr. Lloyd. (Narrative of a Journey from Cawnpoor to the Boorendo Pass, in the Himalaya, by Captain Alexander Gerard and John Gerard, edited by George Lloyd, vol. i. pp. 291, 311, 320, 327, and 341.) Many interesting details regarding some localities may be found in the narrative of A visit to the Shatool, for the purpose of determining the line of perpetual snow on the southern face of the Himalaya, in August, 1822. Unfortunately, however, these travellers always confound the elevation at which sporadic snow falls, with the maximum of the height that the snow-line attains on the Thibetian plateau. Captain Gerard distinguishes between the summits that rise in the middle of the plateau, where he states the elevation of the snow-line to be between 18,000 and 19,000 feet, and the northern slopes of the chain of the Himalaya, which border on the defile of the Sutledge, and can radiate but little heat, owing to the deep ravines with which they are intersected. The elevation of the village of Tangno is given at only 9300 feet, while that of the plateau surrounding the sacred lake of Manasa is 17,000 feet. Captain Gerard finds the snow-line 500 feet lower on the northern slopes, where the chain of the Himalaya is broken through, than towards the southern declivities facing Hindostan, and he there estimates the line of perpetual snow at 15,000 feet. The most striking differences are presented between the vegetation on the Thibetian plateau, and that characteristic of the southern slopes of the Himalaya. On the latter the cultivation of grain is arrested at 9974 feet, and even there the corn has often to be cut when the blades are still green. The extreme limit of forests of tall oaks and deodars is 11,960 feet; that of dwarf birches 12,983 feet. On the plains, Captain Gerard found pastures up to the height of 17,000 feet; the cereals will grow at 14,100 feet, or even at 18,540 feet; birches with tall stems at 14,100 feet, and copse or brushwood applicable for fuel is found at an elevation of upwards of 17,000 feet, that is to say, 1280 feet above the lower limits of the snow-line at the equator, in the province of Quito. It is very desirable that the mean elevation of the Thibetian plateau, which I have estimated at only about 8200 feet between the Himalaya and the Kouen-Lun, and the difference in

advantage, to which sufficient attention has not hitherto been directed. This portion of the surface of the globe affords in the smallest space the greatest possible variety of impressions from the contemplation of nature. Among the colossal mounthe height of the line of perpetual snow on the southern and on the northern slopes of the Himalaya, should be again investigated by travellers who are accustomed to judge of the general conformation of the land. Hitherto simple calculations have too often been confounded with actual measurements, and the elevations of isolated summits with that of the surrounding plateau. (Compare Carl Zimmerman's excellent Hypsometrical Remarks in his Geographischen Analyse der Karte von Inner Asien, 1841, s. 98.) Lord draws attention to the difference presented by the two faces of the Himalaya and those of the Alpine chain of HindooCoosh, with respect to the limits of the snow-line. "The latter chain," he says, "has the table-land to the south, in consequence of which the snow-line is higher on the southern side, contrary to what we find to be the case with respect to the Himalaya, which is bounded on the south by sheltered plains, as Hindoo-Coosh is on the north." It must, however, be admitted that the hypsometrical data, on which these statements are based, require a critical revision with regard to several of their details; but still they suffice to establish the main fact, that the remarkable configuration of the land in Central Asia affords man all that is essential to the maintenance of life, as habitation, food, and fuel, at an elevation above the level of the sea, which in almost all other parts of the globe is covered with perpetual ice. We must except the very dry districts of Bolivia, where snow is so rarely met with, and where Pentland (in 1838) fixed the snow-line at 15,667 feet, between 16° and 17° south latitude. The opinion that I had advanced regarding the difference in the snow-line on the two faces of the Himalaya has been most fully confirmed by the barometrical observations of Victor Jacquemont, who fell an early sacrifice to his noble and unwearied ardour. (See his Correspondance pendant son voyage dans l'Inde, 1828 à 1832, liv. 23, pp. 290, 296, 299.) Perpetual snow," says Jacquemont, "descends lower on the southern than on the northern slopes of the Himalaya, and the limit constantly rises as we advance to the north of the chain bordering on India. On the Kioubrong, about 18,317 feet in elevation, according to Captain Gerard, I was still considerably below the limit of perpetual snow, which, I believe to be 19,690 feet in this part of Hindostan." (This estimate I consider much too high.)

The same traveller says, "To whatever height we rise on the southern declivity of the Himalaya, the climate retains the same character, and the same division of the seasons as in the plains of India; the summer solstice being every year marked by the same prevalence of rain, which continues to fall without intermission until the autumnal equinox. But a new, a totally different climate begins at Kashmir, whose elevation I estimate to be 5350 feet, nearly equal to that of the cities of Mexico and Popayan,' (Correspond. de Jacquemont, t. ii., pp. 58 et 74). The warm and humid air of the sea, as Leopold von Buch well observes, is carried by the mon

tains of Cundinamarca, of Quito, and of Peru, furrowed by deep ravines, man is enabled to contemplate alike all the families of plants, and all the stars of the firmament. There, at a single glance, the eye surveys majestic palms, humid forests of bambusa, and the varied species of musacea, while above these forms of tropical vegetation appear oaks, medlars, the sweetbrier, and umbelliferous plants, as in our European homes. There, as the traveller turns his eyes to the vault of heaven, a single glance embraces the constellation of the Southern Cross, the Magellanic clouds, and the guiding stars of the constellation of the Bear, as they circle round the arctic pole. There the depths of the earth and the vaults of heaven display all the richness of their forms and the variety of their phenomena. There the different climates are ranged the one above the other, stage by stage, like the vegetable zones, whose succession they limit; and there the observer may readily trace the laws that regulate the diminution of heat, as they stand indelibly inscribed on the rocky walls and abrupt declivities of the Cordilleras.

Not to weary the reader with the details of the phenomena which I long since endeavoured graphically to represent,* I soons across the plains of India to the skirts of the Himalaya, which arrest its course, and hinder it from diverging to the Tiibetian districts of Ladak and Lassa. Carl von Hügel estimates the elevation of the valley of Kashmir above the level of the sea at 5818 feet, and bases his observation on the determination of the boiling point of water, (see theil 11, s. 155, and Journal of Geog. Soc., vol. vi. p. 215). In this valley, where the atmosphere is scarcely ever agitated by storms, and in 34° 7′ lat., snow is found, several feet in thickness, from December to March.

*See, generally, my Essai sur la Géographie des Plantes, et le Tableau physique des Régions Equinoxiales, 1807, pp. 80-88. On the diurnal and nocturnal variations of temperature, see Plate 9 of my Atlas Géogr. et Phys. du Nouveau Continent; and the Tables in my work, entitled De distributione geographica Plantarum secundum cœli temperiem et altitudinem montium, 1817, pp. 90-116; the meteorological portion of my Asie Centrale, tom. iii., pp. 212, 224; and, finally, the more recent and far more exact exposition of the variations of temperature experienced in correspondence with the increase of altitude on the chain of the Andes, given in Boussingault's Memoir, Sur la profondeur à laquelle on trouve, sous les Tropiques, la couche de Temperature Invariable. (Ann. de Chimie et de Physique, 1833, t. liii., pp. 225-247.) This treatise contains the elevations of 128 points, included between the level of the sea and the declivity of the Antisana (17,900 feet), as well as the mean temperature of the atmosphere, which varies with the height between 81° and 35° F.

will here limit myself to the consideration of a few of the general results whose combination constitutes the physical delineation of the torrid zone. That which, in the vagueness of our impressions, loses all distinctness of form, like some distant mountain shrouded from view by a veil of mist, is clearly revealed by the light of mind, which by its scrutiny into the causes of phenomena learns to resolve and analyze their different elements, assigning to each its individual character. Thus in the sphere of natural investigation, as in poetry and painting, the delineation of that which appeals most strongly to the imagination, derives its collective interest from the vivid truthfulness with which the individual features are pourtrayed.

The regions of the torrid zone not only give rise to the most powerful impressions by their organic richness and their abundant fertility, but they likewise afford the inestimable advantage of revealing to man, by the uniformity of the variations of the atmosphere and the development of vital forces, and by the contrasts of climate and vegetation exhibited at different elevations, the invariability of the laws that regulate the course of the heavenly bodies, reflected, as it were, in terrestrial phenomena. Let us dwell then for a few moments on the proofs of this regularity, which is such, that it may be submitted to numerical calculation and computation.

In the burning plains that rise but little above the level of the sea, reign the families of the banana, the cycas, and the palm, of which the number of species comprised in the flora of tropical regions has been so wonderfully increased in the present day, by the zeal of botanical travellers. To these groups succeed, in the Alpine valleys and the humid and shaded clefts on the slopes of the Cordilleras, the tree-ferns, whose thick cylindrical trunks and delicate lacelike foliage stand out in bold relief against the azure of the sky, and the cinchona, from which we derive the febrifuge bark. The medicinal strength of this bark is said to increase in proportion to the degree of moisture imparted to the foliage of the tree by the light mists which form the upper surface of the clouds resting over the plains. Everywhere around, the confines of the forest are encircled by broad bands of social plants, as the delicate aralia, the thibaudia and the myrtleleaved andromeda, whilst the Alpine rose, the magnificent

befaria, weaves a purple girdle round the spiry peaks. In the cold regions of the Paramos, which is continually exposed to the fury of storms and winds, we find that flowering shrubs and herbaceous plants, bearing large and variegated blossoms, have given place to monocotyledons, whose slender spikes constitute the sole covering of the soil. This is the zone of the grasses, one vast savannah extending over the immense mountain plateaux, and reflecting a yellow, almost golden tinge, to the slopes of the Cordilleras, on which graze the lama and the cattle domesticated by the European colonist. Where the naked trachyte rock pierces the grassy turf and penetrates into those higher strata of air which are supposed to be less charged with carbonic acid, we meet only with plants of an inferior organisation, as lichens, lecideas, and the brightly-coloured dustlike lepraria, scattered around in circular patches. Islets of fresh-fallen snow, varying in form and extent, arrest the last feeble traces of vegetable development, and to these succeeds the region of perpetual snow, whose elevation undergoes but little change, and may be easily determined. It is but rarely that the elastic forces at work within the interior of our globe, have succeeded in breaking through the spiral domes, which, resplendent in the brightness of eternal snow, crown the summits of the Cordilleras-and even where these subterranean forces have opened a permanent communication with the atmosphere, through circular craters or long fissures, they rarely send forth currents of lava, but merely eject ignited scoriæ, steam, sulphuretted hydrogen gas, and jets of carbonic acid.

In the earliest stages of civilisation the grand and imposing spectacle presented to the minds of the inhabitants of the tropics could only awaken feelings of astonishment and awe. It might perhaps be supposed, as we have already said, that the periodical return of the same phenomena, and the uniform manner in which they arrange themselves in successive groups, would have enabled man more readily to attain to a knowledge of the laws of nature; but as far as tradition and history guide us, we do not find that any application was made of the advantages presented by these favoured regions. Recent researches have rendered it very doubtful whether the primitive seat of Hindoo civilisation-one of the most remarkable phases in the progress of mankind-was actually