sediments. To this areas north east Ram Rock appears to be an eroded basanitic pipe associated with peridotite and pyrometamorphosed Otago Schist xenoliths. The Swinburn area to the south side of State Highway 85 has coarse doleritic textured basaltic volcanics overlying scoria-fall deposits, which in turn overlie Eocene-Oligocene marine sediments. The basalt contains rare xenoliths of peridotite, schist and porcellanitised Cenozoic sediment. North of State Highway 85 there are thin aphanitic basanitic lavas that overlie Miocene sediments that have all been tilted and now mostly dip to the north and northeast. In the Pigroot area at Trig L lavas overlie marine sediments and include an exotic rock of mantle peridotite and crustal gabbro xenolith-bearing phonolite as the cap of Trig L. The northwestern area of the Kakanui Range in north Otago has Siberia Hill as the main eruptive centre with a basanite cap on top of trachybasalt covering a thin layer of Eocene to Oligocene sediments above the Otago Schist. Kattothyrst, about to its east, is a columnar-jointed basanitic plug. Mount Dasher about to the northwest of Kattothyrst, has basanite lavas with an intervening phonotephrite flow on the north east side. The Obelisk has a south end of trachybasalt and basalt at the northern end. Just southwest of Dunedin the Saddle Hill, Jaffray Hill and Scroggs Hill volcanoes are composed of tuff and basaltic trachyandesite, phonotephrite and basanite lava emplaced through coal-bearing sediments and Cenozoic mudstone. Basanite is dominant on Saddle Hill and phonolitic pyroclastic rock underlies lava at Scroggs Hill. An historic underground coal mine is reported to have encountered the feeder pipe at Jaffray Hill. Further to the south west are the volcanoes on the western side of Lake Waihola with at least three vents. Olivine theralite (nepheline gabbro), clinopyroxenite and peridotite have been found there. Relationship to other volcanoes New Zealand's South Island has many extinct volcanic centres with no yet fully agreed tectonic mechanism of formation. They extend in age from the Cretaceous to the Pliocene and outcrop throughout Otago, Canterbury and on the Chatham Islands. The largest single eruptive centre in the South Island is the Banks Peninsula Volcano followed by the Dunedin Volcano but the Dunedin volcanic group contains a much larger monogenetic volcanic field of related eruptives to the later. These volcanic centres can be dormant for tens of millions of years between eruptions. This implies that the mechanism of formation may be