It is possible that the volcanic soil of the table-land may be the cause of this exuberance of salt water. Lake Van, a sheet of salt water 240 miles in circumference, is separated from the equally salt lake Urmiah only by a low range of hills; and there are many pieces of fresh water in that neighbourhood, possibly in similar hollows. Persia is singularly destitute of water; the Lake of Zurrah, on the frontiers of Afghanistan, having an area of 18 square miles, is the only piece of water on the western part of the table-land of Iran. It is evident from the saline nature of the soil, and the shells it contains, that the plains round the Caspian, the Lake Aral, and the steppes, even to the Ural Mountains, had once formed part of the Black Sea; 57,000 square miles of that country are depressed below the level of the ocean—a depression which extends northwards beyond the town of Saratov, 300 miles distant from the Caspian. The surface of the Caspian itself, which is 83 feet 7 inches below the level of the ocean, is its lowest part, and has an area of 18,000 square miles, nearly equal to the area of Spain. In Europe alone it drains an extent of 850,000 square miles, receiving the Volga, the Ural, and other great rivers on the north. It has no tide, and its navigation is dangerous from heavy gales, especially from the south-east, which drive the water miles over the land; a vessel was stranded 46 miles inland from the shore. It is 600 feet deep to the south, but is shallower to the east where it is bounded by impassable swamps many miles broad.[124] The Lake of Eltonsk, on the steppe east of the Volga, has an area of 130 square miles, and furnishes two-thirds of the salt consumed in Russia. Its water yields 29·13 per cent. of saline matter, and from this circumstance is more buoyant than any that is known.[125] The Lake of Aral, which is shallow, is higher than the Caspian, and has an area of 3372 square miles; it has its name from the number of small islands at its southern end, Aral signifying “island” in the Tartar language. Neither the Caspian nor the Lake of Aral have any outlets, though they receive large rivers; they are brackish, and, in common with all the lakes in Persia, they are decreasing in extent, and becoming more salt, the quantity of water supplied by tributaries being less than that lost by evaporation. Most of the rivers that are tributary to the Lake of Aral are diminished by canals, that carry off water for irrigation: for that reason a very diminished portion of the waters of the Oxus reaches the lake. Besides, the Russian rivers yield less water than formerly from the progress of cultivation. The small mountain-lake Sir-i-Kol, in the high table-land of Pamer, from whence the Oxus flows, is 15,600 feet above the sea; consequently there is a difference of level between it and the Dead Sea of nearly 17,000 feet.