Fig. 3

Wegener’s different proposals to illustrate the relationships between the light continental rocks (sial) and the underlying denser rocks (sima) on which the lighter rocks float. a The first illustration of crustal structure and the relationship between “sal” (sial) and sima (Wegener 1912a), on the example of the Java Sea (horizontal and vertical scales equal). b Schematic cross-section of the “lithosphere” (meaning here, light continental rocks = sial) according to the law of isostasy, showing the roots below mountain chains, the flexure caused by glacial loading, the thinning under epicontinental seas and the extreme thinning of the sial under the deep ocean (Wegener 1922). c Schematic view of the disjunctions in the sialic layer (white) caused by continental drift in the extensional mode (Wegener 1922). This illustration could have inspired Argand in his proposals of oceanisation. d A more sophisticated view of the internal structure of the continental basement (sial, white), with pockets of sima as inclusions in the “lithosphere”, a possible source of volcanism (Wegener 1922). This cross-section is the mirror image of the right side of Fig. 3b. e Wegener’s final proposal (Wegener 1929). Light continental rocks (sial) overlying basaltic rocks (sima), the latter absent in some parts of the ocean (oceanisation?), where then sub-simatic rocks form the ocean floor