this evidently exceptional geological catastrophe, the character of the Tchad is clearly that of an immense lagoon whose borders change every month, and of which it is consequently impossible to lay down any strictly accurate map.[87] Lake Tchad lies between lat. 12° 30' and 14° 30' N., long. 13° and 15° 30' S. Its length varies from two hundred to three hundred miles, according to the amount of rainfall and similar circumstances; at its broadest it measures one hundred and seventy miles; and it has an elevation of eight hundred feet above the sea-level. The actual margin of its waters is lined by a deep fence of papyrus and tall reeds, from ten to fourteen feet high. Its islands are densely peopled. Fish and water-fowl abound, and not less do crocodiles and hippopotami. The lake has no outlet, but receives several rivers, of which the Waube and the Shari are the most notable. The country watered by the Niger is also broken up by vast plains which, fertile and glowing in the rainy season, are scorched and withered by the summer heats. The famous port of Kabara, not far from Timbuktù, is several miles from the river, and only accessible for five months in the year at the epoch of the great rains. Beyond this belt of vegetation, this girdle of fertility, Nature wears a sombre aspect--the stony look of a corpse; for the immense Desert of the Sahara begins. The transition from the one region to the other, from the land of plenty to the land of want and famine, from the land of bright lakes, and copious streams, and green pastures, to the land of rocky heights and barren sandy wastes, is as startling as the change which sometimes occurs in human life--the change of a moment, from bustling and exuberant happiness to profound sorrow. It is such contrasts, however, that enable us fully to appreciate the beauty and wealth of Nature. "The scorching winds from arid deserts borne," teach us to prize the balmy breath of the "sweet south" that wanders "o'er a bank of violets." Fresh from the dreary Sahara plain, burnt and scathed by a Tropic sun, we can feel all the loveliness of the woodland and the leafy vale, of each "Melodious plot Of beechen green, and shadows numberless." Thus, in the material world as in the moral and intellectual, the law of compensation prevails, and the wayfarer in the Desert of Life may cheer himself with the recollection that in due time the silence will be succeeded by music, the desolation by beauty, and the wilderness by "Verdurous glooms, and winding mossy ways." CHAPTER II. DESERTS OF THE NEW WORLD:--PRAIRIES, PAMPAS, LLANOS.