The main branch of the river is of the utmost importance when considering the changes wrought upon the surface of the earth through aqueous agencies. Below Ismail it ramifies into a multitude of channels, which change continuously, new channels being excavated, whilst others become choked with alluvial deposits carried down by the floods. Twice the waters of the river are reunited into a single channel before they finally spread out into a secondary delta jutting into the Black Sea. The exterior development of this new land amounts to about twelve miles, and supposing the sea to be of a uniform depth of thirty-three feet, it would advance annually at the rate of 660 feet. Yet, in spite of this rapid increase, the coast, at the Kilia mouth, juts out far less to the east than it does in the southern portion of the delta, and we may conclude from this that the ancient gulf of the sea, now filled up by the alluvial deposits brought down by the Kilia branch, was far larger and deeper than those to the south.[47] On examining a map of the Danubian delta, it will be found that, by prolonging the coast-line of Bessarabia towards the south, it crosses the delta. This is the ancient coast. It rises above the half-drowned plains like an embankment, through which the branches of the river forced themselves a passage to the sea. The alluvium brought down by the Sulina and St. George’s mouths has been spread over a vast plain lying outside this embankment, whilst that carried down through what is at present the main branch forms only a small archipelago of ill-defined islands {161} beyond it. We may conclude from this that the latter is of more recent origin than the other arms. In the course of its gradual encroachment upon the sea, the river has cut off several lakes of considerable extent. On the coast between the mouth of the Dniester and the delta of the Danube there are several lagoons, or _limans_, of inconsiderable depth, the water of which evaporates during the heat of summer, depositing a thin crust of salt. In their general configuration, the nature of the surrounding land, and parallelism of the rivers which flow into them, these sheets of water are very much like the lakes met with more to the west, as far as the mouth of the Pruth. These latter, however, are filled with fresh water, and the sandy barriers at their lower ends separate them not from the Black Sea, but from the Danube. There can be no doubt that these lakes were anciently gulfs of the sea, similar in all respects to the lagoons still existing along the coast. The Danube, by converting its ancient gulf into a delta, separated them from the sea, and their saline water was replaced by fresh water carried down by the rivers. The existing saline lagoons will undergo the same metamorphosis, in proportion as the delta of the Danube gains upon the sea. [Illustration: Fig. 45.—THE DANUBE AND YALOMITZA. Scale 1 : 1,443,000.]