57 



The rounding of the detrital quartz, feldspar, and heavy 

 minerals of these sands is 0„1, Sphericity of this material 

 ranges from 0o70 to 0.80. Organic debris and authigenic 

 minerals are well-rounded and highly spherical. These 

 characteristics are inherent from their mode of formation. 

 Broken shell material is generally angular and exhibits low 

 values of sphericity. 



Occurrence 



Fine quartz-feldspar sand is the most widely distributed 

 sand type in the bay (Fig. 19). It covers most of the area of 

 the shelf and forms the major coarse fraction of the sediment 

 deposited in the two submarine canyons and on the offshore 

 slopes. Even in areas designated as glauconite sands, as much 

 as 70% of the sediment may be of the quartz-feldspar type, and 

 where the content of calcium carbonate increases by an abundance 

 of Forarainifera, the detrital mineral grains are mainly quartz 

 and feldspar. Again, on the offshore slopes, where median 

 diameters are small, the coarse fraction of the sediment is 

 generally fine quartz-feldspar sand. 



The physiography of the shelf areas where this sand type 

 occurs is generally an area of smooth micro-relief. 



Rock-fragment Sand 



Description 



This sand is medium grained, subangular and contains 

 rock fragments that generally are particles of dark schist 

 and fine-grained igneous rock. The rock fragments are acces- 

 sory, however, for the bulk of the sand is made up of quartz 



