16 and 30 percent south of Chincoteague and north of Bethany Beach. 

 Epidote also increases to the north from between 6 and 10 percent off 

 Maryland to between 11 and 15 percent off Delaware. 



By studing 16 vibratory cores and correlating the results with high- 

 resolution seismic reflection data, Sheridan, Dill, and Kraft (1974) were 

 able to map subsurface sediment types on the Delaware inner shelf. They 

 identified the following major sediment types: nearshore marine sand, 

 lagoonal mud and clay, estuarine-shallow marine silt, peat and fringing 

 marsh mud, and gravel and oxidized sand. All of the lithologies except 

 the last were interpreted as Holocene in age. 



Moody's (1964) study was one of the few intensive investigations of 

 ridge and swale topography on the inner shelf. He analyzed the sediments, 

 topography, and changes in shoal configuration on the Delaware inner 

 shelf. The emphasis of his sediment studies is on texture. He notes 

 that nearly all samples are sand or gravelly sand and cites other refer- 

 enced material to show their mineralogic content. The sands are domi- 

 nantly quartz (75 to 80 percent) with 10 to 20 percent altered feldspar. 

 They contain a few percent nonopaque heavy minerals (dominant ly staurolite, 

 sillimanite, tourmaline, and pink garnet) and small amounts of mica, limo- 

 nite, glauconite, calcium carbonate, rock fragments, and organic carbona- 

 ceous material (Shepard and Cohee, 1936; Edsall, 1955; U.S. Army Engineer 

 District, Philadelphia, 1956; Moody, 1964). 



2 . Lithology of Major Sediment Types . 



The lithologic character of Delaware and Maryland inner shelf deposits 

 was determined by macroscopic and microscopic examination of samples from 

 70 vibratory cores varying in length from 2.4 to 9.1 meters (8 to 30 feet). 

 Samples were extracted from cores at 1-foot intervals and cataloged; nearly 

 one-half of the cores were split for detailed logging and photographing. 

 Samples of sand units were selected for textural analysis by sieve and fall 

 velocity techniques. The results of the studies are presented in Appendix 

 B. Core locations are shown in Figure 23 in relation to the fabric of the 

 ridge and swale topography. Core numbers range from 1 to 77; however, 

 core 76 was collected outside of the study area and double-numbered cores 

 (e.g., 24 and 25, 66 and 67) indicate single sites where an effort was 

 made to obtain 12.2 meters of core, twice the standard length of a nominal 

 6.1-meter core. 



Surface and subsurface sediments can be broadly classed into five 

 major sediment types. The main basis for classification is grain-size 

 distribution (modal size and sorting); secondary emphasis is on color and 

 minor variation in grain types. Major sediment types are as follows: 

 type I--medium to coarse, well-sorted sand; type II--fine, well-sorted 

 sand; type III--very fine to fine, poorly sorted sand; type IV--gray mud; 

 and type V--atypical sediments. The last sediment type is a general head- 

 ing to include rarely occurring sediments such as gravels or atypical 

 colored sands or muds. General characteristics of each sediment type are 

 given in Table 4 . 



55 



