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If the size which Herodotus attributes to the Sea of Asoph, which he makes equal to the Euxine[99], had been less vaguely indicated, and if we knew precisely what he meant by the Gerrhus[100], we should there find strong additional proofs of the changes produced by rivers, and the rapidity with which they are made; for the alluvial depositions of rivers alone have, since the time of Herodotus, that is to say, in the course of two thousand and two or three hundred years, reduced the Sea of Asoph[101] to its present comparatively small size, shut up the course of the Gerrhus, or that branch of the Dnieper which had formerly joined the Hypacyris, and discharged its waters along with that river into the gulf called Carcinites, now the Olu-Degnitz, and reduced the Hypacyris itself to almost nothing[102]. We should possess proofs no less strong of the same kind, could we be certain that the Oxus or Sihoun, which at present discharges itself into the lake Aral, formerly reached the Caspian Sea. But we are in possession of facts sufficiently conclusive on the point in question, without adducing such as are doubtful, and without being exposed to the necessity of making the ignorance of the ancients in geography the basis of our physical propositions.[103]