The hypothesis of continental drift has become of increasing interest to geophysicists in recent years. The IUGG Upper Mantle Committee has stated that the hypothesis of continental drift envisages horizontal displacements of the continents over thousands of kilometers, and that it is a principal objective of the Upper Mantle Project to prove whether or not continental drift has occurred. The origin of the hypothesis may be traced to the close similarity in outlines of the coasts on the two sides of the Atlantic Ocean. The theory that the eastern and western hemispheres are drifting apart was expounded in particular by A. Wegener.