4. The Sediment Carpet 

 and the Substratum 



Por millions upon millions of years an incessant snow- 

 fall of tiny particles has been settling over the ocean 

 floor. The origin of these particles has varied. There is 

 among them exceedingly fine-grained dust from the 

 continents, carried seaward by strong winds, especially 

 from the great deserts. There is volcanic ash, blown high 

 up into the stratosphere at explosive eruptions, which 

 has settled slowly from great heights down to the ocean 

 surface. There are, especially in the vicinity of the 

 continents, minute particles of clay or sand carried into 

 the sea by the rivers. There is even — most interesting 

 of components — cosmic dust from interplanetary space 

 and fragments of meteors heated to incandescence 

 during their fiery flight through the upper layers of air. 



In addition to these inorganic particles there are 

 abundant contributions from innumerable marine 

 organisms, mostly of microscopic size, which pass their 

 life in the sunlit surface layers, building up their tiny 

 skeletons or shells from the silica or lime present in the 

 water. After death these remnants, freed from organic 



48 



