There is much evidence of the existence of a system of shear planes in the greatest part of the Earth's crust, and it seems likely that some planetary cause must have brought it about. Two possible causes are investigated here, (1) the decrease of the Earth's flattening because of the slowing down of its rotation by tidal friction and (2) a change of the axis of the flattening because of a movement of the Earth's rotation axis with regard to the crust. Only the latter phenomenon gives a good explanation of the existing system of shear planes. A good correlation is obtained with the Earth's topography, with the distribution of volcanoes, with the gravity fields in several areas, and with most of the evidence about shear planes brought out by the “lineament” tectonicians Hobbs, Sederholm, Daubrée, Sonder, and others.The hypothesis is not in harmony with the continental drift theory of Wegener. At the end of the paper some tentative conclusions are drawn about the origin of the contin