Mesopotamia, the land "in the middle of the rivers," Euphrates and Tigris, consists of two divisions, an upper and a lower. The dividing line crosses from near Hit or His on the Euphrates to below Samarah on the Tigris. Above this line the country is a gently undulating plain of secondary formation at some elevation above the sea. But Lower Mesopotamia is absolutely flat land, an unbroken stretch of alluvial soil, scarcely higher than the Persian Gulf, upon which it steadily encroaches. Chaldea was confined to this Lower Mesopotamia, and was not larger, Rawlinson estimates, than the kingdom of Denmark.[24] It is the monotonous level which first impresses the traveller; but if the season be favourable, he sees this only as the theatre of vast and varied displays of colour, which all visitors vie with one another in describing: "It is like a rich carpet;" "emerald green, enamelled with flowers of every hue;" "tall wild grasses and broad extents of waving reeds;" "acres of water-lilies;" "acres of pansies." There was no such country in ancient times for wheat, barley, millet, and sesame;[25] tamarisks, poplars, and palms; here and there heavy jungle; with flashing streams and canals thickly athwart the whole, and all shining the more brilliantly for the interrupting patches of scurvy, nitrous soil, and the grey sandy setting of the desert with its dry scrub. The possible fertility of Chaldea is incalculable. But there are drawbacks. Bounded to the north by so high a tableland, to the south and south-west by a superheated gulf and broad desert, Mesopotamia is the scene of violent changes of atmosphere. The languor of the flat country, the stagnancy and sultriness of the air, of which not only foreigners but the natives themselves complain, is suddenly invaded by southerly winds, of tremendous force and laden with clouds of fine sand, which render the air so dense as to be suffocating, and "produce a lurid red haze intolerable to the eyes." Thunderstorms are frequent, and there are very heavy rains. But the winds are the most tremendous. In such an atmosphere we may perhaps discover the original shapes and sounds of Ezekiel's turbulent visions--_the fiery wheels; the great cloud with a fire infolding itself; the colour of amber_, with _sapphire_, or lapis lazuli, breaking through; _the sound of a great rushing_. Also the Mesopotamian floods are colossal. The increase of both Tigris and Euphrates is naturally more violent and irregular than that of the Nile.[26] Frequent risings of these rivers spread desolation with inconceivable rapidity, and they ebb only to leave pestilence behind them. If civilisation is to continue, there is need of vast and incessant operations on the part of man.