GUTENBERG is not a geologist but, as a geophysicist, he is directly interested in several of the broader questions of geology. He has been impressed by the simple way in which Wegener’s drift theory seems to solve many geological problems, but he finds it impossible to accept that theory in its entirety. He has, therefore, tried to formulate another theory which is more in accordance with geophysical data, and which still solves the same geological problems. “Continental Spreading,” a name suggested by Dr. Harold Jeffreys, expresses very clearly its dominant feature.