CONDITION OF THE OCEAN FLOOR 275 



128. Ocean Depths. The greatest depth thus far found 

 in the ocean is nearly six miles. This was found in the 

 Pacific Ocean near the Ladrone Islands. The greatest 

 depth in the Atlantic Ocean thus far discovered is a little 

 over five miles at a point north of Porto Rico. The aver- 

 age depth of the sea is probably about two and one half 

 miles. 



Although the pressure at the bottom of the ocean must 

 be tremendous, yet so incompressible is water that a cubic 

 foot of it weighs but little more at the bottom of the sea 

 than it does at the top. Thus a body which sinks will in 

 time reach the bottom no matter what the depth may be. 

 At a depth of two miles the pressure is over 300 times as 

 much as at the surface of the water and here, as we have 

 already found, it is about 15 pounds to the square inch. 



If a bag of air which had a volume of 300 cubic inches 

 at the surface were sunk in the ocean to a depth of two 

 miles, it would have a volume of less than a cubic inch, 

 and the pressure upon it would be several tons. It thus 

 happens that deep sea fishes when brought to the surface 

 have the air in their swimming bladders so expanded that 

 the bladder is often blown out of their mouths. 



129. Condition of the Ocean Floor. The ocean floor is a 

 vast, monotonous, nearly level expanse whose dreary, 

 slimy and almost lifeless surface is enveloped in never- 

 ending night and is pressed upon by a vast weight of 

 stagnant, frigid water. Here and there volcanoes rise 

 upon it with gradually sloping, featureless cones, and some- 

 times a broad wavelike swell reaches within a mile or so 

 of the surface. Such a swell extends along the center 

 of the Atlantic Ocean through Ascension Island and the 

 Azores. 



There are no hills and vales, no mountain ranges having 

 sharp peaks and deep valleys. Gradually rising ridges 



