which have to be considered in connection with the westerly drift of the continents. Various authors, as E. H. L. Schwarz and Wettstein, among others, have claimed the friction of the tidal waves, which will be produced in the solid earth through the attraction of the sun and moon, for a rotation to the west of the whole crust of the earth over the interior. It is also frequently supposed that the moon had formerly a more rapid rotation, but it was retarded by the tidal friction caused by the earth. It is also easy to see that this retardation of a planetary body by tidal friction must especially effect its upper surface, and lead to a slow, sliding movement of the whole crust, or of the individual continental blocks. There remains only the question as to whether such tides exist at all. The deformation of tides in the solid body of the earth, detected by the horizontal pendulum, is, according to Schweydar, of another kind, namely, elastic, and can thus not be directly drawn upon for the explanation. But nevertheless I believe it possible that even these elastic tides give the impulse to a slight progressive displacement of the crust, due to the viscosity of the sima, which accumulates from day to day by an amount which is certainly very slight, and so not at all apparent in the daily measurements, but which can nevertheless lead to considerable displacements in the course of millions of years. For it is beyond question that we cannot regard the earth as being completely elastic in relation to the tidal forces. In my opinion this question cannot yet be considered as settled, simply because the elastic nature of the measurable daily tides in the solid earth has been established.
In another way (which, however, is again referable to the attraction of the sun and moon), namely, on the basis of the precession theory of the earth’s axis,
