SONE, or Son, a river of central India which has been identified with the Erannoboas of the Greek geographers. With the exception of the Jumna it is the chief tributary of the Ganges on its right bank. It rises in the Amarkantak highlands about 3500 ft. above sea-level, the Nerbudda and Mahanadi also having their sources in the same table-land. From this point it flows north-west through an intricate mass of hills, until it strikes the Kaimur range, which constitutes the southern wall of the Gangetic plain. Here it turns east and continues in that direction until it falls into the Ganges about 10 m. above Patna, after a total course of 465 m. Its upper waters drain about 300 m. of wild hilly country, which has been imperfectly explored; while in its lower section of 160 m. it traverses the British districts of Mirzapur, Shahabad, Gaya and Patna. The Sone canals, fed by the river, form a great system of irrigation in the province of Behar. The headworks are situated at Dehri about 25 m. below the point where the river leaves the hilly ground. The weir across the Sone at this point is believed to be the longest constructed in a single unbroken piece of masonry, the length between abutments being 12,469 ft. A main canal is taken off on either bank of the river, and each of these is divided into branches, according to the requirements of the ground. The system consists of some 370 m. of canals and 1200 m. of distributaries, irrigating 555,000 acres. The Sone canals were begun in 1869, and came into operation in 1874; they form a valuable protection to the rice crop of Behar.