Complex sentence: The Blyth & Tyne Railway was a railway in Northumberland chiefly constructed to link the collieries in Ashington, Seghill and Blyth to the river Tyne at Percy Main.
Split into simpler sentences: The Blyth & Tyne Railway was a railway in Northumberland. It was chiefly a coal-carrying network linking collieries in Ashington, Seghill and Blyth to the river Tyne at Percy Main.