Complex sentence: The NBR encouraged the promotion of the Esk Valley Railway, which opened as far as Polton in 1867; the line primarily served paper mills adjacent to the river, and because of the terrain was unsuitable for connecting to the pits.
Split into simpler sentences: The NBR encouraged the promotion of the Esk Valley Railway, which opened as far as Polton in 1867. The line primarily served paper mills adjacent to the river, and because of the terrain was unsuitable for connecting to the pits.