The Danube, with its extensive terrace lands, faces the east, and has, therefore, very different relations to European history from the Rhine. It is a double-headed river, and one of its head-streams, the one which bears the name of the river proper, extends almost to the Rhine basin; while the other, the Jura, has its source in Grisons, and hard by the head-waters of the Rhine. As the Danube connects the Caspian and Black Sea basin with western Europe, and the largest part of the Asiatic immigrations have followed its course, the Danube has become the great avenue between Europe and Asia. Celts, Teutons, and Romans were mingled even before Christ, in Noricum, Vindelecia, Bavaria, and Suabia. How many tribes may have been crowded westward by these, is unknown to us. The same fate has happened to the people who settled there before Christ, and the inroads of the Huns, Goths, and other tribes of similar origin, scattered the older inhabitants over all Central Germany. We know, too, that Sclavic, Hungarian, and Turkish incursions followed, each one dispossessing wholly or in part the one which preceded it. All great rivers and river systems have had a similar influence on the course of civilization. There is not a single type feature in the world which has not contributed its part to the advance of the human race; no one is without its place and its function. PART III. The Configuration of the Continents. All the divisions of the earth, taken together in their internal and external connections, in their mutual action and reaction, constitute the unity of the globe, and make apparent that it is a simple organism, designed and created by divine skill, and intended to be the home of a race whose culture should, in the course of centuries, unfold from the most simple beginnings to the most complex and elaborate perfection. We have already seen that the surface of the earth is naturally divided into three typical features—highland, lowland, and the transition terraces between them. From the vertical and horizontal combination of these result the most of the geographical forms which are the subject of our study. They form what we may, for convenience, call the bas-relief of the globe.