Fig. 6

Convection currents presented by Arthur Holmes in the article published in German in Basel (Holmes, 1930). Fig. 2: situation of a continent before continental drift—below an idealised continental block (lightly striped, above A), presence of convection currents inside the Earth, rising at A and plunging downwards at B and C. Fig. 3: pulling apart of the continent—the splitting of the continental block leads to the formation of oceans and islands (above A), whilst at B, the enriched Sial forms a rising border zone in front of a foredeep-trench with the formation of a geosyncline behind. Fig. 4: another situation, above the descending current at C—a turbulence develops at D due to heat transport from A to C, causing mountain building and a submerged marginal zone towards the old ocean