ARGAN, or ERGON, a river of Tartary, in the country of the Mongols, which rises from a lake called Dalai, or Koulan-nor, situated in long. 119° 14'. E. and lat. 49° N. It is considered to be the original source of the Amur, and by the treaty of Nerchinsk, concluded in 1690, is established as the mutual boundary between the Chinese and Russian empires, from its source to its mouth.