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 greatér 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 
