88 



of coarse detrital material derived from the land areas; 

 therefore, there is less dilution of calcareous material 

 offshore. Thus, the amount of CaC03 is inversely propor- 

 tional to the supply of inorganic detritus at any point on 

 the bottom. The size of calcareous material is not dependent 

 upon currents and turbulence to the extent that terrigineous 

 sediments are, so that skeletal remains of sand-size and 

 larger may accumulate where currents are very weak. Con- 

 versely, the coarseness of some of the shells allows this 

 material to accumulate where fine grained material cannot, 

 i,e., in regions of strong currents and turbulence. In 

 deeper seaward areas, shells (primarily the tests of Forami- 

 nifera) form the major portion of the coarse fraction of the 

 sediment, probably as a result of a small contribution of 

 detrital material which in other areas would normally dilute 

 the organic contribution. 



Organic Matter 



Almost all elements found in organic compounds are also 

 found in inorganic material. As a result, it is difficult 

 to separate pvire organic matter. Since carbon is the princi- 

 pal constituent of organic matter, it is generally used as 

 an index of the amount of organic material. The abundance of 

 organic carbon varies between 50 and 60 per cent in organic 

 debris and if the total quantity of organic matter is desired, 

 the per cent carbon must be multiplied by an appropriate 

 factor which varies between 1,7 and 1,9, The choice of the 

 factor is difficult to make because the value depends upon 



