10 THE OCEAN FLOOR 



remarkable fact that the very greatest depths are not 

 found in the central parts of the oceans but are concen- 

 trated within curiously formed furrows or trenches 

 which run close to and parallel with continental coasts 

 or island festoons. In these trenches are found record 

 deeps like the Emden Deep and the Johnson Deep in 

 the Philippine Trench off the west coast of Mindanao, 

 with soundings of very nearly 35,000 feet, and the still 

 greater Challenger Deep southeast of Guam, with a 

 maximum depth of 36,000 feet. This is considerably 

 more than the height above sea level of the world's 

 highest mountain peak. Mount Everest. 



Turning to the Indian Ocean, we find in the western 

 part, where most of the banks and islands are located, a 

 great submarine ridge running south to north from the 

 Antarctic Continent. The eastern part of the Indian 

 Ocean is in general of a greater and more uniform depth 

 and has only one deep trench, the great Sunda Double 

 Trench, running along the south coast of Java with a 

 maximum depth of about 25,000 feet. 



Such are, in brief, the main features of the great 

 cavities in the earth's crust which are at present filled 

 with ocean water. The question naturally arises whether 

 this has always been so. In other words, what is the 

 history of the oceans in relation to the continents? 



Here oceanographers must confess their ignorance. 

 What little we believe we know is largely conjecture — 

 theories put forward by students of geophysics, geology, 

 zoogeography, and phytogeography (the last two from 



