First, there will be the changes in latitude. Let us visualize briefly the consequences of a displacement of the whole crustal shell of the earth. This idea has nothing whatever to do with the much discussed theory of drifting continents, according to which the continents drifted separately, in different directions. The crust, in this case, will move as a single unit, the whole crust at the same time. If a gentle push is exerted horizontally on the earth's crust, to shove it in a given direction, and if the push is maintained steadily for a long time, it is highly probable that the crust willl be displaced over this plastic and viscous lower layer. It is known that a viscous material will yield easily to a comparatively slight pressure exerted over a long period of time, even though it may act as a solid when subjected to a sudden pressure, such as an earthquake wave. The rock at that depth is supposed to have high viscosity that is, it is fluid but very stiff, as tar may be. Moreover, it is thought that pressure at that depth renders the rock extremely plastic, so that it will yield easily to pressures. Immediately under the crust is a layer that is thought to be extremely weak, because it is, presumably, too hot to crystallize.
The crust is made of comparatively rigid, crystalline rock, but it is fractured in many places, and does not have great strength. Estimates of its thickness range from a minimum of about twenty to a maximum of about forty miles.
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