Let me remark at the outset that considerable progress has been made in the investigation of this question, both from its scientific and its historical side. Lyell, and Prestwich, with the geologists who have followed them, laid a solid foundation of knowledge regarding the later mutations in the physical geography of Britain. Guest, Pearson, Freeman, Green, and others, have shown in how many ways the historical development of the people has been influenced by the topographical features of the country. Yet in spite of all that has been done, I do not hesitate to say that we are still only a little way beyond the threshold of this wide subject. No one has realised more vividly at once the importance of the inquiry and the imperfection of the available data than the late Mr. J. R. Green. He would fain have been able to reconstruct the successive phases through which our landscapes have passed since the dawn of history; and he did more in this respect with his materials than perhaps any other living man could have done. But the detailed evidence was wanting to him; and it has still in large measure to be gathered before the ideal of the historian can be reached. Now, I am desirous of insisting upon the fact that this detailed evidence does not lie shut up from the reach of all but the practised man of science and the mature historian. Much of it, whether in the literary or scientific domain, may be gleaned by any young undergraduate who will bring to the task quickness of observation and accuracy of judgment. As the harvest is abundant but the labourers few, I would fain enlist the sympathy and co-operation of any who may be able and willing to help. There are four obvious sources of information regarding former conditions of the land. First comes the testimony of historical documents, then that of place-names, next that of tradition, and lastly, that of geological evidence.