10 



UNDERWATER GUIDE TO MARINE LIFE 



3. The Deep-Sea Bottom. This lies below the great majority of the sea's 

 area. It is here that the most spectacular canyons on earth sink and the 

 greatest mountains on earth rise. 



OCEANIC PROVINCE 



OCCANIC TRENCH 



Fig. I. Veatures and zones of the sea. 



In the western United States are many well-known mountains, one of 

 which is Pike's Peak. It rises to 9,000 feet from a plateau of 5,000 feet high, 

 a total of 14,000 feet. Mt. St. Elias in Alaska is one of the very largest of 

 mountains on earth, rising from sea level to 18,000 feet, twice the height 

 of Pike's Peak. Mt. Everest rises to over 29,000 feet, but its base is very high, 

 so it actually is not as large in sheer volume as is St. Elias. By contrast, 

 Mauna Kea of Hawaii rises a total of 31,000 feet directly from the sea 

 bottom (almost 14,000 feet from sea level) and is so huge that it forms the 

 greater part of the largest of the Hawaiian Islands. There are many huge 

 mountains under the sea at least as large as Pike's Peak that never even reach 

 the surface. 



Mountain ranges of the sea are no less spectacular. By far the longest range 

 on earth is undramatically called the "Mid- Atlantic Ridge," which is 10,000 

 miles long. It begins off the coast of southern Africa and runs unbroken to 

 Iceland, showing a few times above the surface in such islands as the Azores 

 and Ascension. 



Perhaps the most spectacular and mysterious of the deep-sea features are 

 the trenches, steep canyons usually found close to shore lines and continental 

 shelves, which plummet to depths of up to 35,000 feet (Mariana Trench). 

 The deepest North American trench is the Puerto Rican Trench with a 

 depth of 30,246 feet. Trenches are usually deeply filled with layers of sediment 

 a mile or more in thickness. Without these, the trenches would be even deeper. 



The bottom of the deep sea is usually covered with a monotonous layer 

 of red clay where a few hardy animals make their homes. Hesse, and others 



