In the north, a chain of mountains, covered with snow, extends from the province of Yunan to China, and its ramifications form two great divisions, between which is situated the fertile valley of Siam. Another chain stretches towards the west, as far as the Malay peninsula. The great river Menam, already mentioned, traverses the level country from north to south, taking its rise in the southern slopes of the mountains of Yunan, and empties itself into the Gulf of Siam. It is the Nile of this region, the great fertility of which is owing to the annual overflowing of its waters, an event eagerly looked for by the inhabitants, and welcomed as a blessing from Heaven. The Menam begins to rise in the month of June, and in August the inundation reaches its height, and then the waves of the ocean, opposing themselves to the current, force the waters of the river back upon its banks. The lands situated towards the middle of the great plain receive most benefit from this operation of nature, the higher districts being too much surrounded by mountains, while the lower are impregnated with so much salt water as to render the cultivation of rice difficult. If the regular inundations are, as a general rule, productive of immense benefit, they now and then, as in Egypt, lay waste the country: thus, for example, that of 1851 destroyed all the sugar-plantations; and the water, to a depth of three or four feet, resting on the earth for some time, a large number of cattle perished, the rice-crops suffered seriously, and many valuable fruit-trees were carried away. Some years afterwards, however, in accordance with nature’s beneficent law of compensation, the produce was only the more abundant. The ancient annals of Siam relate that, about the seventh century, Chinese junks used to ascend the stream as far as Sang-Khalak, a distance of 120 leagues from the sea; at present it is only navigable for 30 leagues at most. This alteration has arisen from a gradually-increasing collection of sand and alluvial deposit--a process which goes on in some of our western rivers, as, for instance, the Rhine and the Meuse. The low grounds, as is usually the case in hot climates, are less healthy than the mountainous districts, and the forests especially are the seat of malignant fevers. Several other rivers, and numberless canals, fringed with bamboos and fruit-trees, round which fly a multitude of birds, give a pleasing aspect to the country, which is bounded on the horizon by richly-wooded hills. The rivers are rich in fish, which, in addition to rice, forms the principal food of the people. [Illustration: Drawn by M. Sabatier, from a Sketch by M. Mouhot. PERFORATED ROCK IN THE ISLE OF EBOULON, GULF OF SIAM.]