The Danube, to the north of the Dobruja, performs an amount of geological work, in comparison with which that of the Maritza, the Strymon, and Vardar sinks into insignificance. That mighty river annually conveys to the Black Sea a volume of water far in excess of that which is carried down the rivers of all France, and the solids which it holds in suspension are sufficient to cover an area of ten square miles to a depth of nine feet. This enormous mass of sand and clay is annually deposited in the swamps and on the banks of the delta, and the slow but steady growth of the latter is thus sufficiently explained. Even the ancients {137} anticipated a time when the Black Sea would be converted into a shallow pond abounding in sand-banks, and it must, therefore, afford some consolation to our mariners to be told that six million years must pass before the alluvium carried down the river will fill the whole of the Black Sea. [Illustration: Fig. 39.—THE DELTA OF THE DANUBE. Scale 1 : 1,500,000.] The large triangular plain which the Danube has conquered from the sea has not yet fully emerged from the waters. Lakes, and the remains of ancient bays, half-obliterated branches of the Danube, and the ever-changing beds of rivulets, have converted this delta into a domain, half land, half sea. More elevated tracts, consolidated by the attack of the waves, rise here and there above the melancholy mire and reeds, and bear a dense vegetation of oaks, olives, and beeches. Willows fringe most of the branches of the river which take their winding course through the delta. Twenty years ago the Danube had six mouths; it has now only three. After the Crimean war the Western powers determined that the Kilia branch, which conveys to the Black Sea more than half the volume of the Danube, should thenceforth form the boundary between Rumania and Turkey. The Sultan thus possesses not only the whole of the delta, which has an area of about 4,000 square miles, but also the only mouth of the river which makes the possession of that territory of any value to him. The mouth of the Kilia is closed by a bar of sand, which does not even permit small vessels to enter it. {138}