small block of Madagascar (which combines with its drift from the poles, to give it a north-easterly movement). Perhaps the late East African fault system, of which the separation of Madagascar certainly only forms a part, might be brought into connection with the westward drift, although in this case we are no longer dealing with island festoons, but with large blocks. On the west coast of Africa the Canary and Cape Verde Islands seem, it is true, to have been first detached in very recent times, and in this manner to have departed towards the west; but this small westward advance of the sima may well be accounted for as a result of the general flow of the sima at the opening-up of the Atlantic Ocean. This could only mean that the sima surface of the Atlantic was drawn out like rubber in the progress of its opening, or that there was a predominant flow of sima into the rift.
Whether all the details of the displacements can be explained by these two components of the drift from the poles and of the westward drift, must, indeed, remain undecided. The chief movements in the earth’s crust, however, are apparently fairly well accounted for by them.
It is also to be expected that the arrangement of the rifts in the sial crust should be systematic, for indeed rifts and displacements are inter-related. The drift towards the west would correspond to meridional rifts. The drift from the poles could also occur, in the presence of meridional rifts, especially if these are continued up to the pole. It has already been said that, as a matter of fact, we can recognize a tendency to a meridional direction of the trough-faults and rifts; and the East African fault system, the Rhine Valley, and especially the great Atlantic separation, were given as examples. The prolongation to the Pole may be
