Keechelus andesite series 4000 ft.
All the volcanic rocks of these islands are submarine stratified tuffs which are penetrated here and there by andesite or diabase dikes.
The lavas and ashes ejected by these volcanoes consist of liparite, dacite, andesite and basalt.
Howson andesite 250 ft.
The rolled crystals of sapphire occur, with garnet and other minerals, in glacial deposits, and have probably been derived from dykes of igneous rocks, like andesite and lamprophyre.