Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/157

Rh of the earth can exert such an influence on the behaviour of its materials need not, therefore, remain unanswered. We know that steel loses its rigidity under such pressures as we can mechanically produce, and becomes plastic. We cannot erect an indefinitely high column of steel without reaching a limit at which the foot of this column begins to flow. If we imagine an entire continental margin of steel, its uppermost portion would certainly remain rigid, but the lower layers would become plastic under the pressure of the mass lying above it, and would flow out laterally. Thus steel is no longer a solid body in such large dimensions as that of the earth. Indeed, it may be said that for such dimensions no solid body exists, and that all bodies have the property of viscid fluidity, but that the times needed for deformation will be different, according to their coefficients of viscosity. On this last point it is very instructive to note that Schweydar arrived at the result that the simasphere is about 10,000 times as rigid as sealing-wax at the temperature of a room. If a stick of sealing-wax be thrown on the floor, it breaks into splintery fragments; but if it be left supported only at two points, a bending can be noticed after some weeks; and after some months the unsupported portions will hang practically vertical. Geologically speaking, sealing-wax is thus of such mobility at ordinary temperatures that we cannot use it at all for the explanation of geological phenomena. If the sima has a viscosity coefficient 10,000 times as large as that of sealing-wax, then a month for the sealing-wax is equivalent to a thousand years for the sima. And this is a period of time which corresponds more with geological changes. We need not therefore draw the conclusion from Schweydar’s figures that the earth, because it has the same viscosity as steel, behaves as if it were a rigid body. This is only