planting the flag of France on the Gulf of Mexico at its mouth.  The Tupi Indians of South America, a genuine water-race, moved from their original home on the Paraguay headstream of the La Plata down to its mouth, then expanded northward along the coast of Brazil in their small canoes to the estuary of the Amazon, thence up its southern tributary, the Tapajos, and in smaller numbers up the main stream to the foot of the Andes, where detached groups of the race are still found.[635] So the migrations of the Carib river tribes led them from their native seats in eastern Brazil down the Xingu to the Amazon, thence out to sea and along the northern coast of South America, thence inland once more, up the Orinoco to the foot of the Andes, into the lagoon of Maracaibo and up the Magdalena.  Meanwhile their settlements at the mouth of the Orinoco threw off spores of pirate colonies to the adjacent islands and finally, in the time of Columbus, to Porto Rico and Haiti.[636] [See map page 101.]

[Sidenote:  Historical importance of seas and oceans influenced by their debouching streams.]

So intimate is this connection between marine and inland waterways, that the historical and economic importance of seas and oceans is noticeably influenced by the size of their drainage basins and the navigability of their debouching rivers.  This is especially true of enclosed seas.  The only historical importance attached to the Caspian’s inland basin is that inherent in the Volga’s mighty stream.  The Mediterranean has always suffered from its paucity of long river highways to open for it a wide hinterland.  This lack checked the spread of its cultural influences and finally helped to arrest its historical development.  If we compare the record of the Adriatic and the Black seas, the first a sharply walled cul de sac, the second a center of long radiating streams, sending out the Danube to tap the back country of the Adriatic and the Dnieper to draw on that of the Baltic, we find that the smaller sea has had a limited range of influence, a concentrated brilliant history, precocious and short-lived as is that of all limited areas; that the Euxine has exercised more far-reaching influences, despite a slow and still unfinished development.  The Black Sea rivers in ancient times opened their countries to such elements of Hellenic culture as might penetrate from the Greek trading colonies at their mouths, especially the Greek forms of Christianity.  It was the Danube that in the fourth century carried Arianism, born of the philosophic niceties of Greek thought, to the barbarians of southern Germany, and made Unitarians of the Burgundians and Visigoths of southern Gaul.[637] The Dnieper carried the religion of the Greek Church to the Russian princes at Kief, Smolensk, and Moscow.  Owing to the southward course of its great rivers, Russia has found the crux of her politics in the Black Sea, ever since the tenth century when the barbarians from Kiev first appeared before Constantinople.  This sea has had for her a higher economic importance than the Baltic, despite the latter’s location near the cultural center of western Europe.