The doctrine that the present ocean basins came into being at an early stage of the earth’s history we owe especially to James D. Dana† and Charles Darwin,‡ though there have been many followers. The facts and supposed facts on which this theory was founded have for the most part either been modified or given a different interpretation during the time which has since elapsed. Moreover, the new seismology—the study of earthquakes from a distant station—seems now to be furnishing new and valuable data for a solution of the question of age of the present ocean depressions. Many of the arguments once urged in support of the antiquity of the present basins, interpreted in the clearer light of today, inveigh against it. These arguments have perhaps nowhere been better stated than in the anniversary address of the late Professor W. T. Blanford before . . .