A mathematician who turned to geology and the study of igneous rocks and volcanoes, Daly was a professor at Harvard University. In the 1920s he was one of the very few supporters in America of the theory of continental drift. He proposed that drift was caused by continental ‘downsliding’ due to gravity, above a molten mantle which had the properties of glass. It was Daly who first suggested, in 1936, that submarine canyons may be excavated by suspension currents. See also turbidity currents.