THE Surface History dealt with in this book is based directly upon two great recent advances in our knowledge of the earth's crust: the Radioactivity of the Rocks and Isostasy. The nature of both are herein discussed and explained. Both are recognized to-day by most men of science as facts. These two fundamental elements of the surface constitution of the globe lead naturally to certain great events which at long intervals are recurrent in the history of the earth’s surface.