 Six aqueducts were required to allow the canal to cross the River Irwell , the River Tonge and four roads . On the Bolton arm these were Hall Lane Aqueduct , Fogg 's Aqueduct and the larger <unk> Aqueduct , all of which have since been demolished . Hall Lane Aqueduct was damaged by mining subsidence and replaced in 1884 – 1885 . It was demolished in 1950 . The Salford arm flowed over Prestolee Aqueduct , then Clifton Aqueduct , and finally the smaller <unk> 's Lane Aqueduct ( since demolished ) . 
