IX THE SEA 357 



composed of materials, brought down by 

 rivers or washed from the shore, coarser near 

 the coast, and tending to become finer and 

 finer as the distance increases and the water 

 deepens. The bed of the Atlantic from 400 

 to 2000 fathoms is covered with an ooze, or 

 very fine chalky deposit, consisting to a great 

 extent of minute and more or less broken 

 shells, especially those of Globigerina. At 

 still greater depths the carbonate of lime 

 gradually disappears, and the bottom consists 

 of fine red clay, with numerous minute parti- 

 cles, some of volcanic, some of meteoric, origin, 

 fragments of shooting stars, over 100,000,000 

 of which are said to strike the surface of our 

 earth every year. How slow the process of 

 deposition must be, may be inferred from the 

 fact that the trawl sometimes brings up many 

 teeth of Sharks and ear-bones of Whales (in 

 one case no less than 600 teeth and 100 ear- 

 bones), often semi-fossil, and which from their 

 great density had remained intact for ages, 

 long after all the softer parts had perished 

 and disappeared. 



The greatest depth of the Ocean .appears 



