Complex sentence: The impact threw the last four coaches of the Dundee train over the sea wall, the last 2 broke away completely and ended up in the Firth of Tay, fortunately the tide was out.
Split into simpler sentences: The impact threw the last four coaches of the Dundee train over the sea wall. The last 2 broke away completely and ended up in the Firth of Tay; fortunately, the tide was out.