40 



(grain diameters between 2 and .062 mm) is determined using 

 the sedimentation method described by Emery (1938). Grain- 

 size distribution of the silt and clay is determined by the 

 standard pipette method (Krumbein and Pettijohn, 1938, p. 165- 

 170), The total weight of silt and clay is determined from 

 the pipette analysis. From these data the per cent of gravel, 

 sand, silt, and clay are determined and a cumulative curve of 

 the grain-size distribution is drawn from which the median 

 diameter and Trask's sorting coefficient were determined. 



Calcium Carbonate 



In a sediment calcium carbonate is considered to be the 

 material soluble in cold, dilute hydrochloric acid. This 

 value is determined by slowly adding the acid to a dried and 

 weighed sample until effervescence ceases. After this the 

 remaining sediment is washed with distilled water and any 

 remaining acid decanted off. The remaining sediment is dried 

 and weighed to determine the per cent calcium carbonate (dry 

 weight) for the entire sample. 



Organic Carbon 



Organic carbon content can be determined by the Allison 

 (1935) method of oxidizing a 500 mg sample of sediment with 

 chromic acid and the excess chromic acid back-titrated with 

 0.2 N ferrous ammonium sulfate. Under the conditions of the 

 determination, free carbon is not oxidized and carbonates, 

 being already oxidized, are not affected. Although this 

 method is rapid, convenient, and duplications check within 

 one per cent, it is not an absolute method because it assumes 



