Here, the narrow channel of Carnley Harbour (the Adams Straits on some maps) separates the main island from the roughly triangular Adams Island (area approximately ), which is even more mountainous, reaching a height of at Mount Dick. The channel is the remains of the crater of an extinct volcano, and Adams Island and the southern part of the main island form the crater rim. The main island features many sharply incised inlets, notably Port Ross at the northern end.