Modem geologists think in terms of revolutions. Each revolution built a number of mountain chains in different parts of the world. The most violent revolutionary changes are to be looked for in the building of the highest mountain chain, the Himalayas, and Dr. E. B. Bailey, the Director of the British Geological Survey, has recently interpreted the findings in this range of two Swiss geologists, Heim and Gansser, and the Indian geologist, Wadia. Dr. Bailey has not yet unreservedly accepted the theory which is to-day the great geological heresy, but may be generally accepted in another generation, the theory that the continents have drifted for thousands of miles over melted matter below them like slag on the top of a mass of molten metal. Geologists are becoming more and more ready to believe in very large changes in the earth's surface in the remote past. Much the same changes have taken place in anthropological theory.