119 



Much information on the general natxire of the source 

 rocks can be determined from the mineralogy and organic con- 

 stituents of sediments. For example, the presence of Forami- 

 nifera of Miocene or Pliocene age in rocks of Recent age would 

 indicate that the contributing sources included rocks of the 

 older ageSo Mineralogically, suites of heavy minerals, 

 including minerals typical of igneous and metamorphic rocks, 

 would indicate the relative importance of these sources. 



For the purposes of tabulation of sediment contributions 

 and losses, a general budget has been noted in Table III. 



Of the listed contributing items, it is possible to 

 indicate those of least importance. Gains from wind, chemical 

 precipitation, organic production, sewage and industrial wastes, 

 and artificial fill can be regarded as minor. Erosion of sub- 

 marine rock outcrops is also probably relatively unimportant 

 due to the restricted area of such outcrops in areas of active 

 erosion by waves, and currents. Wave erosion of sea cliffs is 

 not known, but papers by Revelle and Shepard (1939), Grant and 

 Shepard (1940), and Shepard and Grant (1947) would indicate that 

 this contribution is minor. It becomes evident that the major 

 contributing sources are littoral drift and stream-carried 

 sediments. The relative importance of drift versus stream trans- 

 port is not well-defined at present. The effect of Point Dume 

 as a sediment transport barrier to the north is controversial, 

 for example ■ Trask (1952), Hand in Cl95lX Trask ^1955). At the 

 northern end of the bay the evidence leans tov ard a southerly 

 movement of sand around the Point Dume area of unknown volume. 



