INTRODUCTION To the structure of the body of scientific thought the nearest parallel is found in that of a well constructed edifice, with each part so designed as to fit accurately and without intervening space to other parts in its neighborhood, and all reared upon acommon foundation. Were our knowledge perfect this ideal might be realized and no harm result, but we are accustomed to erect the superstructure over the ac- cepted fundamental tenets of the science of our time, just as though history did not warn us that on the long upward course of the growth of knowledge the dominant thought of one period has often been abandoned in the next. A survey of the past will show that the great advances in scientific thought have followed the discovery of new points of view, viewpoints which have offered new outlooks over the field ahead. Such a survey will tell us further that our mistakes in the past have arisen very largely because from each new coign of vantage, as it has been attained, the attempt has been not only to adjust the nearer field, but to sketch in strong lines the hazy distances as well as the nearer landscape. Better than tarrying so long at each sta- tion would it have been to advance over the field already mapped so as to secure a better viewpoint and bring up the distant horizon. Our etapes have been both too long and much too infrequent. If the foundation of our structure is to be removed, it becomes necessary for the superstructure to be taken down, and, before rebuilding, such material as can be used from the old structure must be fitted to the form of the new basement. Far more than is generally supposed, the recent abandonment of the nebular hypothesis to account forthe origin of the universe, must carry with it a rewriting of our science. This is particularly true of geology for all that concerns seismology, volcanology and the whole subject of the growth of continents and mountains. The present tune is there- fore an opportune one for supplying to these fields a dis- cussion which can be harmonized with the newer viewpoint and be independent of the abandoned groundwork of the science. For nearly a score of years the author has concerned him- self with certain of the fundamental questions of theo- retical geology which are in one way or another connected with the growth of continents and mountains, and these studies moving along different directions were converging upon important results when they were interrupted by the distractions of the World War…