I say then the Pontus has long been in process of being filled up with mud, and that this process is actually going on now: and further, that in process of time both it and the Propontis, assuming the same local conditions to be maintained, and the causes of the alluvial deposit to continue active, will be entirely filled up. For time being infinite, and the depressions most undoubtedly finite, it is plain that, even though the amount of deposit be small, they must in course of time be filled. For a finite process, whether of accretion or decrease, must, if we presuppose infinite time, be eventually completed, however infinitesimal its progressive stages may be. In the present instance the amount of soil deposited being not small, but exceedingly large, it is plain that the result I mentioned will not be remote but rapid. And, in fact, it is evident that it is already taking place. The Maeotic lake is already so much choked up, that the greater part of it is only from seven to five fathoms deep, and accordingly cannot any longer be passed by large ships without a pilot. And having moreover been originally a sea precisely on a level with the Pontus, it is now a freshwater lake: the sea-water has been expelled by the silting up of the bottom, and the discharge of the rivers has entirely overpowered it. The same will happen to the Pontus, and indeed is taking place at this moment; and though it is not evident to ordinary observers, owing to the vastness of its basin, yet a moderately attentive study will discover even now what is going on.
For the Danube discharging itself into the Pontus by several mouths, we find opposite it a bank formed by the mud discharged from these mouths extending for nearly a thousand stades, at a distance of a day's sail from the shore as it now exists; upon which ships sailing to the Pontus run, while apparently still in deep water, and find themselves unexpectedly stranded on the sandbanks which the sailors call the Breasts. That this deposit is not close to the shore, but projected to some distance, must be accounted for thus: exactly as far as the currents of the rivers retain their force from the strength of the descending stream, and overpower that of the sea, it must of course follow that to that distance the earth, and whatever else is carried down by the rivers, would be projected, and neither settle nor become fixed until it is reached. But when the force of the currents has become quite spent by the depth and bulk of the sea, it is but natural that the soil held in solution should settle down and assume a fixed position. This is the explanation of the fact, that, in the case of large and rapid rivers, such embankments are at considerable distances, and the sea close in shore deep; while in the case of smaller and more sluggish streams, these sandbanks are at their mouths. The strongest proof of this is furnished by the case of heavy rains; for when they occur, rivers of inferior size, overpowering the waves at their mouths, project the alluvial deposit out to sea, to a distance exactly in proportion to the force of the streams thus discharging themselves. It would be mere foolish scepticism to disbelieve in the enormous size of this sandbank, and in the mass of stones, timber, and earth carried down by the rivers; when we often see with our own eyes an insignificant stream suddenly swell into a torrent, and force its way over lofty rocks, sweeping along with it every kind of timber, soil, and stones, and making such huge moraines, that at times the appearance of a locality becomes in a brief period difficult to recognise.
This should prevent any surprise that rivers of such magnitude and rapidity, flowing perpetually instead of intermittently, should produce these effects and end by filling up the Pontus. For it is not a mere probability, but a logical certainty, that this must happen. And a proof of what is going to take place is this, that in the same proportion as the Maeotic lake is less salt than the Pontus, the Pontus is less so than the Mediterranean. From which it is manifest that, when the time which it has taken for the Maeotic lake to fill up shall have been extended in proportion to the excess of the Pontic over the Maeotic basin, then the Pontus will also become like a marsh and lake, and filled with fresh water like the Maeotic lake: nay, we must suppose that the process will be somewhat more rapid, insomuch as the rivers falling into it are more numerous and more rapid. I have said thus much in answer to the incredulity of those who cannot believe that the Pontus is actually being silted up, and will some day be filled; and that so vast a sea will ever become a lake or marsh. But I have another and higher object also in thus speaking: which is to prevent our ignorance from forcing us to give a childish credence to every traveller's tale and marvel related by voyagers; and that, by possessing certain indications of the truth, we may be enabled by them to test the truth or falsehood of anything alleged by this or that person.
