Section 3(1)(a) in The Bihar And Uttar Pradesh (Alteration Of Boundaries) Act, 1968
(a)there shall be added to the State of Bihar--(i)all the territories of Ballia district of the State of Uttar Pradesh lying between the fixed boundary and the deep stream of the river Ghaghra, and(ii)all the territories of that district lying between the fixed boundary and the deep stream of the river Ganga, and