In spite of the importance of the constructive forces which are still building up the mountains, much of the finest scenery of the cordillera is due to the destructive forces of erosion. The majestic Columbia Canyon, like others of its kind, is the work of running water. Glaciers also have done their part. During the glacial period the forces which control the paths of storms did not give to the cordillera region such an abundance of snow as was sifted down upon Laurentia. Therefore no such huge continental glaciers have flowed out over millions of square miles of lower country. Nevertheless among the mountains themselves the ice gouged and scraped and smoothed and at its lower edges deposited great moraines. Its work today makes the cliffs and falls of the Yosemite one of the world's most famous bits of scenery. This scenery is young and its beauty will pass in a short time as geology counts the years, for in natural scenery as in human life it is youth that makes beauty. The canyons, waterfalls, and geysers of the cordillera share their youth with the lakes, waterfalls, and rapids due to recent glaciation in the east. Nevertheless, though youth is the condition of most striking beauty, maturity and old age are the condition of greatest usefulness. The young cordillera with its mountains still in the making can support only a scanty population, whereas the old eastern mountains, with the lines of long life engraved upon every feature, open their arms to man and let him live and prosper. It is not enough that we should picture merely the four divisions of the land of our continent. We must see how the land meets the sea. In low latitudes in both the Old World and the New, the continents have tended to emerge farther and farther from the sea during recent geological times. Hence on the eastern side of both North and South America from New Jersey to Brazil the ocean is bordered for the most part by coastal plains, uplifted from the sea only a short time ago. On the mountainous western side of both continents, however, the sea bottom shelves downward so steeply that its emergence does not give rise to a plain but merely to a steep slope on which lie a series of old beaches several hundred and even one thousand feet above the present shore line. Such conditions are not favorable to human progress. The coastal plains produced by uplift of the land may be fertile and may furnish happy homes for man, but they do not permit ready access to the sea because they have no harbors. The chief harbor of Mexico at Vera Cruz is merely a little nick in the coast-line and could never protect a great fleet, even with the help of its breakwater. Where an enterprising city like Los Angeles lies on the uplifted Pacific coast, it must spend millions in wresting a harbor from the very jaws of the sea.