SEDIMENT CARPET 



51 



the red clay sometimes takes on the character of radio- 

 larian ooze. Calcareous remains of larger marine or- 

 ganisms, like sharks' teeth and ear bones of whales, 

 frequently occur in the red clay. Highly curious products 

 of the chemistry of great depths are the so-called 

 "manganese nodules" — concretions built up by ac- 

 cumulation or accretion of ferric hydroxide and man- 



Fig. 20. Manganese ncdiile halved 



ganese peroxide around a nucleus, say a shark's tooth 

 or fragment of pumice. These manganese nodules are 

 products of immensely slow growth, the rate of which it 

 has been possible to measure by radioactive methods. 



Two of the most difficult problems of deep-sea re- 

 search are determining the rate of sedimentation and 

 explaining the stratification often found in cyhndrical 

 cores raised from deep-sea deposits. The methods used 

 for studying and dating such records of the deep and 



