 He proposed in 1931 that the Earth's mantle contained convection cells which dissipated heat produced by radioactive decay and moved the crust at the surface.His "Principles of Physical Geology", ending with a chapter on continental drift, was published in 1944.Geological maps of the time showed huge land bridges spanning the Atlantic and Indian oceans to account for the similarities of fauna and flora and the divisions of the Asian continent in the Permian period but failing to account for glaciation in India, Australia and South Africa.