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Show 1900] PHYSIOGRAPHY 7 gateway to the interior, hive conspired to place New York beyond competition in the development of Atlantic ports. Delaware Bay is the estuary of the Delaware River; and Chesapeake Bay, still farther south, receives the Susquehanna, the Potomac, and the James. Neither bay compares as a harbor with New York, but they have been of great moment, nevertheless, in the early and later history of America. From the Chesapeake southward to the extremity of Florida the indentations are fewer, smaller, and shallower, but are of great historical importance. NThe Gulf of Mexico is notable not only as the receiver of the Mississippi drainage, but as an element in modifying the climate of the country by its situation and by the ocean currents to which it gives rise. Of superlative importance not only as barriers to the spread of population, but also as influences modifying climatic conditions, are thevymountain-ranges of a continent. N[ n North America the most striking relief feature is the so - called Cordillera, an immense mountain chain stretching along the western area from Central America to Alaska. \ In reality it is a great plateau'with a breadth of one thousand miles in the United States and with an elevation of from five to ten thousand feetA Upon this broad and lofty base rise various mountain-ranges running longitudinally north and south and reaching their greatest average heights in the Rocky Mountains of Colorado and in the Sierra Nevadas |