In addition to the offshore data, three auger borings were made 30 

 meters below mean low water (MLW) on central Assateague Island in June 

 1974. These borings were obtained for comparison with and interpreta- 

 tion of published borehole logs and for correlation with the inner shelf 

 sediment column. 



3. Field Data Collection Procedures . 



a. Approach . The general approach to the field study was to gather 

 large quantities of acoustic reflection data, supplemented by physical 

 samples (cores) which provided a continuous network throughout the study 

 area. This large data base was then used to determine group character- 

 istics of shelf features and to generalize the subsurface configuration 

 and lithofacies. 



Survey tracklines for the 1970 study were laid out in two line pat- 

 terns: grid or reconnaissance lines. A grid pattern with a line spacing 

 of either 1.6 or 3 kilometers (1 or 2 miles), was used to cover areas 

 where a more detailed development of bottom and subbottom conditions was 

 needed. Off northern Delmarva Peninsula, lines were laid out both paral- 

 lel and perpendicular to the pervasive north-northeast trending ridges or 

 shoals to obtain cross sections of those features. Off the coast of 

 Delaware and Delaware Bay, reconnaissance lines were surveyed to provide 

 a basis for correlation with published studies of the areas and for com- 

 parison of the shelf structure off the headland region of the Delmarva 

 Peninsula with that of the barrier island section. Selection of core 

 sites was based on a continuing review of the seismic profiles as they 

 became available during the survey. Tracklines and core locations are 

 shown in Figures 2 and 3. 



After a preliminary analysis of the data, a detailed survey was plan- 

 ned for selected parts of the ridge and swale topography of the Maryland 

 inner shelf. Tracklines were laid out to give three or four crossings of 

 each shoal so that detailed information could be obtained on internal 

 structures and the surface configuration of the ridges. 



b. Navigation . Position location was controlled during the 1970 

 survey by using a Motorola Range Positioning System (RPS) and during the 

 1974 survey by using a Motorola Mini-ranger. These systems accurately 

 locate a vessel within two fixed reference points. The equipment oper- 

 ates on the same basic principle as a noncoherent pulse radar, utilizing 

 an X-band interrogator unit on the survey vessel and two radar transpond- 

 ers positioned at reference points on land. Elapsed time between the 

 interrogation and transponder response provides the basis for determining 

 the range to each of the transponders. Range to range information from 

 the transponders is triangulated to provide a position fix. RPS is 

 capable of operating at line-of-sight ranges up to 93 kilometers (50 

 nautical miles), and with appropriate calibration the accuracy is better 

 than 15 meters (45 feet) . 



The interrogator uses a time-delayed, coded pulse to interrogate the 

 transponders which prevents interference from other radar signals in the 



