380 Introduction to the Study of Science 



In even the best natural American harbors channels must 

 be widened and deepened for the largest ships. The entrance 

 to the New York harbor through what is called the Ambrose 

 Channel has been dredged to give a depth of forty feet at low 

 tides and 1000 feet width at its narrowest part. The dan- 

 gerous rocks at Hell Gate on the East River were removed 

 years ago by blasting. Where natural facilities are inadequate 

 for harbors, breakwaters of enormous size are built. One 

 breakwater at San Pedro, the harbor for Los Angeles, Cali- 

 fornia, is 9000 feet long and cost approximately $4,000,000. 

 Canals are cut from the sea into fresh-water bodies, where 

 harbors are readily constructed to supplement limited ocean 

 frontage and facilities. 



Docks and piers. Piers must be built to accommodate the 

 largest ships, and equipped with mechanical appliances to 

 facilitate the handling of freight. The harbors along the 

 Great Lakes are perhaps the most completely equipped. Large 

 freight steamers, as many as thirty in a line, may be loaded 

 simultaneously with from 10,000 to 15,000 tons of iron ore 

 each in less than two hours, and unloaded in about four hours. 

 The docks project a quarter of a mile into the lakes. The 

 machinery for handling grain and flour, ores, coal, and lumber 

 is the most modern and efficient. In ocean harbors piers are 

 being rapidly improved and new piers being constructed. The 

 eight 1000-foot piers being built on the North River at New 

 York will accommodate the largest transatlantic express steamers 

 contemplated. At Boston, New Orleans, San Francisco, and 

 Seattle, harbors and increased dockage are being steadily pro- 

 vided to meet the growing demands of modern shipping. 



VIII. INLAND WATERWAYS 



172. River improvement. The improvement of rivers 

 may be illustrated by the work done on the Mississippi. Like 

 many others running through low land, this river overflows 

 at certain seasons. The destruction of property and the hazard 



