The thermobarometry of garnet lherzolite and pyroxenite xeno-liths from kimberlitic explosion pipes and volcanoes has been used to determine the geotherms, values of the surface heat flow, and the thickness of the lithosphere in regions of Archean orogeny (the Kaapvaal Craton, South Africa and Lesotho, and the Siberian Platform in the vicinity of the Udachnaya and Mir pipes), Proterozoic orogeny (Somerset Island, N.W.T., Canada; Gibeon Province, Namibia; and the Colorado Plateau, USA), and Paleozoic orogeny (southeastern Australia, and the Hangay Highlands, Mongolia). In each case, during the period of volcanism, the geotherm remains, as before, conductive through the full thickness of the lithosphere, but consists of two branches: a stationary low-temperature branch and a disturbed high-temperature branch, although not everywhere represented by xenoliths. It may be demonstrated that the minerals of the peridotite association enclosed in diamonds, were equilibrated at temperatures and pressures which prev...