Broadly speaking, one half of France is mountainous, and the other flat or undulating. All the mountains are on the eastern half, the high grounds of Normandy and Brittany being scarcely more than hills. The whole country might, for some purposes, be considered as an inclined plane, for in travelling from the Alps on the eastern frontiers to the Atlantic coast the altitudes (omitting the valley of the Rhone) are constantly decreasing. Thus, with the exception of the Rhone, which carries the snow-waters of the Bernese and Pennine Alps, the Vosges and the Jura chains, into the Mediterranean, the waters of nearly the whole of the more habitable three-quarters of the country drain westwards to the Bay of Biscay and the English Channel. Most of this immense reticulation of river and stream is included in the three great systems of the Seine, the Loire, and the Garonne. The Adour drains the triangle between the Pyrenees and the Garonne; the Charente waters the Plain of Poitou between the Garonne and the Loire, but both are of small account in comparison to the vast areas included in the basins of the great rivers. Both the Rhone and the Garonne are of foreign birth, the first beginning life at the foot of the great Rhone Glacier in Switzerland, feeding on her snows and glaciers all the year round, and the second rising in a Spanish valley of the Pyrenees. [Illustration: THE CHATEAU OF AMBOISE ON THE LOIRE.] The Loire, the longest of her rivers, is, however, entirely a possession of France. It is, like the Seine, a cause of very much anxiety on account of its inconstancy. At one season of the year it inundates large areas with its superabundance, and at another it is capable of running so low that only mere streams flow between the sand-banks. So unfortunately situated is the city of Tours in times of flood that it has found it necessary to surround itself with a protective dyke. The chief cause of sudden inundations is when the flood-waters of two or three tributaries conspire to pour in their contributions to the main channel simultaneously, and only when these headstrong young things are held in check will there be any hope of a fairly regular level of water in the main course. Two centuries ago (1711) the need for curbing the flood-waters was recognised so clearly that a dam was constructed at Pinay, a village 18 miles above Roanne. It held up 350 to 450 million cubic feet of water, and has been very successful in maintaining the supply of water in the river-bed during seasons of drought, as well as checking the violence of the floods. In recent times three other dams have been built, two of them near the busy industrial centre of St. Etienne, but until several others have been constructed the flood-waters cannot be held in check.