originally the name of the fertile spots in the Libyan Desert, where there are springs or wells and more or less vegetation, but now applied to any fertile tract in the midst of a waste, and often used figuratively. The oases of northern Africa are generally river valleys, the waters of which are for the most part underground, or depressions, surrounded by short ranges of hills, from which small brooks descend, sometimes forming lakes. In recent times oases have been formed in the Northern Sahara and in the desert regions of the United States by the sinking of artesian wells. There are many important oases in the Western Sahara, in the Libyan Desert, in Arabia, in Persia and in the Desert of Gobi in Central Asia. In ancient times the most celebrated oasis was that to the west of Egypt, containing the temple of Jupiter Ammon, now called the Oasis of Siwah. See DESERT.