The writer derives formulas for plastic buckling and shows how development of geosynclines requires 20 to 40 million years of relatively quiet evolution until, with continuing compressive stress, the catastrophic stage is reached which can bring about great folding and overthrusting of less competent surface layers. During this entire process the plastic part of the crust is thickening. The phenomenon has greater velocity in the ocean than in the continents. The result of this difference of velocity is that a geosyncline on the border between continent and ocean must be asymmetric; the continent appears to override the ocean floor.

When the compressive stress vanishes, relaxation of crustal stresses and a beginning of readjustment to isostatic equilibrium take place. If this relaxation occurs before the catastrophic stage is reached, a high mountain range comes into being without much folding (e.g., the Atlas Mountains). If relaxation takes place afterward, it leads to a high folded mountain range (e.g., the Alps).

The equations explain belts of strong negative anomalies, e.g. in the Indonesian Archipelago, and also the mean positive anomaly of about 30 mgals found over the whole area.

In a brief discussion of the last part of the history of geosynclines the writer advocates the hypothesis that mountains are attacked not only by erosion at the surface, but also by melting and spreading of the crustal root. The migration of this root material under the “foreland” is thought to be responsible for a rising there, as has for example been the case during the formation of the European Mittelgebirge north and west of the Alps.