OCEAN 



1333 



OCEAN 



bed. In the beginning of things the entire 

 earth may have been covered by the sea, for 

 in New England and Alabama and hundreds 

 of other inland regions geologists find shell fos- 

 sils embedded in the rock, bearing silent wit- 

 ness to their ocean birth. The sea, however, 

 take? daily tribute from the land in the form 

 of sand, gravel and mud brought to it by the 

 rivers. The coarser sand and gravel, being 

 heavy, are deposited fairly close to shore, while 

 the finer sand and mud are washed far out. 

 These continental deposits, as they are called. 

 form the continental shelf, and beyond it the 

 'iiental slope, and are carefully indicat..! 

 on navigators' charts so that wrecks may be 

 avoided. 



Plant and Animal Life. Sunlight cannot 

 penetrate the water for more than a quarter of 

 a mile, approximately, and therefore in deep- 

 >cean there is no plant life. Where the 

 depth is not beyond the limits to which light 

 can travel, however, there is great richness and 

 variety of verdure pastures of moss, forests of 

 tangled seaweed, gardens and ferneries of other 

 :igc and interesting marine plants, as luxu- 

 riant as any on earth and far more fascinating. 



There is no need for sight where it is abso- 

 lutely dark, and therefore the fish living in the 

 very deepest parts of the ocean have no eyes. 

 At lesser depths, however, there are vividly- 

 colored phosphorescent fish which shed a radi- 

 ance like that of the glowworm and constitute 

 a "street-lighting department" that gives its 

 service friee to the fish public of their subma- 

 rine community. Since there is no vegetation 

 to feed them, the fish of the deep sea exist by 

 preying upon one another, and many tragedies 

 of nature are staged in these dark waters. 



greater the depth, the heavier the pres- 

 sure of the water, the pressure increasing at the 

 rate of a ton to the square inch for every thou- 

 sand fathoms (6,000 feet) of depth. This means 



that fish living on the bottom of the ocean near 

 the island of Mindanao are supporting a weight 

 of nearly six tons upon every square inch of 

 their bodies. Fish adapted to withstand a cer- 

 tain pressure cannot live where the pressure is 

 either greater or less. If they should attempt 

 to swim deeper they would be crushed by the 

 weight of the water, and when they approach 

 too near the surface they burst. 



Why There Is Icy Water at the Equator. 

 The surface water of the ocean varies in tem- 

 perature with the latitude, so we find the hot- 

 test water (about 80) at the equator, and the 

 coldest at the poles. At a depth of several 

 hundred feet, however, the ocean, even in the 

 tropics, becomes extremely cold. This icy water 

 has drifted down from the poles, spreading its 

 chilling effect over the entire sea. In the low- 

 est depths the temperature is very close to 

 freezing point ; but there is no danger that the 

 ocean will ever freeze because the water is in 

 perpetual motion through waves, tides and cur- 

 rents, and also because the warm water at the 

 equator, constantly rising to the top, keeps the 

 general temperature from dropping too low. 



The Origin of the Ocean's Salt. The old idea 

 has been that the salt in the sea was not there 

 originally but was brought to it little by little. 

 throughout the ages, by the rivrrs which washed 

 it out of the land. In the process of evapora- 

 tion the moisture was drawn up, leaving the 

 salt behind and thus gradually concentrating 

 it in the ocean. The best-supported modern 

 theory, however, is that the ocean has been salt 

 from the very beginning of time. The proof 

 offered is the great similarity between the salts 

 found in the ocean and those present in the 

 gaseous matter ejected from the interior of tin- 

 earth during a volcanic eruption, and the great 

 difference between the salt of ocean water and 

 that of inland salt lakes formed by the evapora- 

 tion of river water. L.M.B. 



Ocean Currents 



Strange as it may seem, there arc great 

 streams flowing through the ocean and some of 

 them arc almost as distinctly divided from the 

 surrounding waters as arc the rivers from the 

 land. These currents constitute a regular sys- 

 tem of circulation in each ocean; the Atlantic 

 and Pacific each have two systems, one north- 

 ern and the other southern. According to 

 perature, ocean currents are classified as warm 

 and cold ; according to position they are su 

 current or dccp-sca currents. Drift is a gen- 



movement of water on the surface, and it 

 has no distinct bounding lines. A current whose 

 waters arc distinctly separated from surround- 

 ing waters is called a stream. 



Cause and Movements of Currents. The chief 

 cause of ocean currents is the sun, which warms 

 the water at the surface and also hastens evapo- 

 ration; the latter increases in rapidity as the 

 if orial regions are approached. Other causes 

 arc tides, irregularities of the coast line, wimU 

 and the rotation of the earth. As water cools 



