In 1822 an important work appeared, which followed the same method in the scientific investigation of the history of the earth that had already proved the most fertile--the _ontological_ method, or the principle of "actualism." It consists in a careful study and manipulation of _actual_ phenomena with a view to the elucidation of the analogous historical processes of the past. The Society of Science at Göttingen had offered a prize in 1818 for "the most searching and comprehensive inquiry into the changes in the earth's crust which are historically demonstrable, and the application which may be made of a knowledge of them in the investigation of the terrestrial revolutions which lie beyond the range of history." This prize was obtained by Karl Hoff, of Gotha, for his distinguished work, _History of the Natural Changes in the Crust of the Earth in the Light of Tradition_ (1822-34). Sir Charles Lyell then applied this _ontological_ or _actualistic_ method with great success to the whole province of geology; his _Principles of Geology_ (1830) laid the firm foundation on which the fabric of the history of the earth was so happily erected. The important geogenetic research of Alexander Humboldt, Leopold Buch, Gustav Bischof, Edward Süss, and other geologists, were wholly based on the empirical foundation and the speculative principles of Karl Hoff and Charles Lyell. They cleared the way for purely rational science in the field of geology; they removed the obstacles that had been put in the path by mythological fancy and religious tradition, especially by the Bible and its legends. I have already discussed the merits of Lyell, and his relations with his friend Charles Darwin, in the sixteenth and seventeenth chapters of my _Natural History of Creation_, and must refer the reader to the standard works on geology for a further acquaintance with the history of the earth and the great progress which dynamical and historical geology have made during the century.