The inner firth's northeast end forms a junction with several other arms of the sea, namely Loch Linnhe, the Lynn of Lorne, Loch Etive, and the Sound of Mull. Loch Spelve and Loch Don on the Isle of Mull and Loch Feochan on the mainland are inlets of the Firth of Lorn. On the southeast side, there are also several channels and sounds in the Slate Islands. The Ordnance Gazetteer of 1882 cites a length of from the intersection of Loch Linnhe and the Sound of Mull, with widths of from , inclusive of the islands on the east side, such as Kerrera and the Slate Islands. The west side is an ample deep-water channel leading ultimately inland to the Caledonian Canal.