The transitional form between stream and pelagic inlet found in every river mouth is emphasized where strong tidal currents carry the sea far into these channels of the land.  The tides move up the St. Lawrence River 430 miles (700 kilometers) or half way between Montreal and Quebec, and up the Amazon 600 miles (1,000 kilometers).  Owing to their resemblance to pelagic channels, the estuaries of the American rivers with their salty tide were repeatedly mistaken, in the period of discoveries, for the Northwest Passage to the Pacific.  Newport in 1608 explored the broad sluggish course of the James River in his search for a western ocean.  Henry Hudson ascended the Hudson River almost as far as Albany, before he discovered that this was no maritime pathway, like the Bosporus or Dardanelles, leading to an ulterior sea.  The long tidal course of the St. Lawrence westward into the heart of the continent fed La Salle’s dream of finding here a water route to the Pacific, and fixed his village of “La Chine” above the rapids at Montreal as a signpost pointing the way to the Indies and Cathay.  In the same way a tidal river at the head of Cook’s Inlet on the Alaskan coast was mistaken for a Northeast Passage, not by Captain Cook but by his fellow officers, on his Pacific voyage of 1776-1780; and it was followed for several days before its character as a river was established.[632]

[Sidenote:  Sea navigation merges into river navigation.]

Rivers have always been the great intermediaries between land and sea, for in the ocean all find their common destination.  Until the construction of giant steamers in recent years, sea navigation has always passed without break into river navigation.  Sailing vessels are carried by the trade wind 600 miles up the Orinoco to San Fernando.  Alexander’s discovery of the Indus River led by almost inevitable sequence to the rediscovery of the Eastern sea route, which in turn ran from India through the Strait of Oman and the Persian Gulf up the navigable course of the Euphrates to the elbow of the river at Thapsacus.  Enterprising sea folk have always used rivers as natural continuations of the marine highway into the land.  The Humber estuary and its radiating group of streams led the invading Angles in the sixth century into the heart of Britain.[633] The long navigable courses of the rivers of France exposed that whole country to the depredations of the piratical Northmen in the ninth and tenth centuries.  Up every river they came, up the Scheldt into Flanders, the Seine to Paris and the Marne to Meaux; up the Loire to Orleans, the Garonne to Toulouse and the Rhone to Valence.[634] So the Atlantic rivers of North America formed the lines of European exploration and settlement.  The St. Lawrence brought the French from the ocean into the Great Lakes basin, whose low, swampy watershed they readily crossed in their light canoes to the tributaries of the Mississippi; and scarcely had they reached the “Father of Waters” before they were