seismic reflection unit I (Fig. 6) and type C sand is characteristic of 

 the upper (sampled) part of this unit. It is not known if the unit below 

 the part sampled by cores is of similar lithology. Seismic reflection 

 profiles show unit I to be within 1.5 meters (5 feet) of the shelf floor 

 in most places and to crop out locally. Cores also indicate a thin over- 

 burden and in the locale of core 42 (Fig. 2) the unit crops out on the 

 shelf floor. 



Type C sand is composed mostly of very fine to fine quartz particles 

 of angular shape and low sphericity (Fig. 18). Phosphorite and glauconite 

 are common accessory minerals; glauconite is more abundant in some type C 

 samples than in any other inner shelf deposit but is very rare in other 

 samples. Calcium carbonate elements consist mostly of foraminiferal 

 tests, which in some samples comprise about half the particles. Mollusk 

 shell fragments, echinoid spines, and ostracod carapaces are also present 

 in relatively small amounts. 



Type C sand, usually darker than type A or B, is typically dark 

 grayish brown (10 yr 4/2) and uniform. The material tends to be silty, 

 partly due to very small foraminiferal tests, and dry samples develop a 

 slight coherence. 



b. Coarse-Grained Sediments . The coarse-grained sediments found in 

 the study area comprise a heterogeneous group of quartz sands, shelly 

 sands, and shell gravels which usually occur in thin and discontinuous 

 patches on the shelf floor or beneath a thin surficial layer. Deposits 

 of this group are generally too thin to be resolved on available seismic 

 reflection records and their distribution and extent are poorly known. 



Most coarse-grained deposits can be classified into two broadly 

 defined types (D and E), depending on the amount of shell present. It 

 is probable that the material represents a number of discrete deposits 

 which are not closely related in origin and may have formed at different 

 times, although most appear to have been placed under marginal marine 

 environmental conditions . 



(1) Type D . Medium to coarse quartz sand and shelly sand (less 

 than 30 percent shells) are grouped as type D sediment. These sands are 

 heterogeneous in character (Fig. 19) and occur in a patchy distribution 

 throughout the study area in both surficial and shallow subsurface depos- 

 its. In some cases, medium surficial sands appear to be localized coarser 

 facies of type A sand. Where this is probable, the core log description 

 includes the modifier "shelf facies." Other deposits of this type may be 

 related to some of the type E shelly sand deposits, differing only in 

 shell content. 



In general, type D sediment consists predominantly of quartz sand 

 which is less angular and more spherical than types A, B, and C. This 

 is due to the better rounding of the large grains which comprise a sub- 

 stantial part of the material . The finer grain-size fraction is more 

 angular. Locally, the sand contains silt, usually in small amounts, but 



42 



