Complex sentence: The Pentland Firth is a seaway which separates Orkney from the mainland of Scotland; it is wide between Brough Ness on the island of South Ronaldsay and Duncansby Head in Caithness.
Split into simpler sentences: The Pentland Firth is a seaway between Orkney and the mainland of Scotland. It is wide between Brough Ness on the island of South Ronaldsay and Duncansby Head in Caithness.