



The geographic line that separates the andesite-dacite-rhyolite rock association of the Pacific margin from the olivine-basalt-trachyte rock association of the Pacific Basin islands is known as the andesite line. This line, mainly determined petrographically, runs on the western side of the Pacific from Alaska to east of New Zealand via Japan, the Marianas, the Palau Islands, the Bismarck Archipelago, the Fiji Islands, and the Tonga Islands. East of the Pacific the line is less well defined but probably follows the west coasts of North and South America; the line’s position in the South Pacific has not been determined.