Perplexing as are all problems connected with geological time, there has naturally appeared much more hope of determining the length of the period that has elapsed since the close of the great Glacial episode in the Northern Hemisphere, the period in which, indeed, we may be said to live, seeing that many processes that can be observed in action may be supposed to have gone on without interruption from the disappearance of the ice to the present day. It has proved, however, scarcely less difficult than the other problems of geological chronology. Many methods have been applied, and the results reached have been hardly less varied than the methods.