hundreds of metres above, and behind the pole some hundreds of metres below the position of equilibrium. The greatest gradient (order of magnitude 1 km. for a quadrant of the earth) would prevail in the meridian of the displacement of the pole at its point of intersection with the equator, and another nearly as large at both the poles. Forces are thereby set free which draw the masses from the too high to the too low areas, and these forces are many times the normal force of the drift from the pole, which corresponds, in the case of the continental blocks, to a gradient of only 10 to 20 m. for a quadrant of the earth. These forces do not act only on the continental blocks as the force of the drift from the poles does, but also on the sima lying beneath, which is more liquid, and perhaps brings about equilibrium under the more rigid crust. But so long as this gradient exists—the transgressions and regressions bear witness to its existence—the force must also operate on the continental blocks, and must therefore cause displacements and folds of the latter, even if these movements are possibly smaller than the corresponding movements of the more liquid material beneath them. In the case of the apprehension being confirmed that the normal force of the drift from the poles is only sufficient for the displacement of continents in the sima, but not for their foldings, I think that we have a source of force in this deformation of the earth’s figure caused by the wanderings of the poles which, in any circumstances, is sufficient to do the work of folding.
This explanation becomes particularly probable through the circumstance that both the greatest systems of folds to be considered in this connection, namely, the equatorial folds of the Carboniferous and of the Tertiary, were formed in exactly those times in which we must assume, on other grounds, especially rapid and
