From Creech St Michael westwards, the B&ER had followed the gently flowing valley of the River Tone. But just east of Wellington, the river moved further west up the steep sides of the Blackdown Hills. Brunel chose to follow a smaller valley eastwards, and pass under the Blackdowns further west, through a place called White Ball, a hill made up of easy to dig white sandstone (NB: next to it is Red Ball, a hill of red sandstone). This route would reduce the need for additional tunnelling, and allow connection with and traffic from Wellington. However, the choice also meant the construction of a long inclined bank, with a tunnel at its peak.