to the usually irregular surface of the submarine hills and ridges. Bathy- 

 metric data and seismic reflection profiles generally do not provide 

 enough information to delineate the mounds; however, the characteri- 

 stics of surveyed known mounds are topographically distinct and should be 

 identifiable on fathometer records. Other similar features may occur in the 

 the study area which are not revealed by existing data. 



c. Submarine Hills and Ridges . 



(1) Inshore Submarine Hills and Ridges . Groups of predominantly 

 rugged hills and ridges are common off rocky stretches of coast (B areas 

 in Fig. 5). A large group occurs in the approaches to Boston Harbor, 

 mostly to the south of Broad Sound. These nearshore hills arid ridges are 

 characteristically of high relief with steep flank slopes. Some of the 



w — ° prominent hills breach the water surface to form islets; a rugged 

 L om topography is created where the hills are closley grouped. 



(2) Offshore Submarine Hills and Ridges . A large group of 

 submarine hills and ridges occurs in a roughly linear configuration 

 extending from the central to the northeastern part of the study area 

 (C area in Fig. 5). In general, these features are larger (in plan 

 view), have less relief and gentler side slopes than the inshore hills and 

 ridges. Some of these features have a ramplike profile with one flank 

 rising steeply from the sea floor and the opposite flank sloping at a 

 gentle gradient. A few isolated hills and ridges occur elsewhere but most 

 of these features are in C area; the bottom is usually level between the 

 individual hills. 



d. Connecting Slopes . In places, extensive sections of bottom with 

 different characteristic elevations are connected by relatively steep 

 slopes leading from one level to the other. Two of these slopes are of 

 considerable extent and are shown in Figure 5 as terrain element D. Both 

 slopes, although irregular and not well defined in places, can be traced 

 for several miles. 



The largest connecting slope lies outside the study limits; the upper 

 part is shown in the bathymetric chart (Fig. 4). This broad, moderately 

 sloping incline descends from the eastern part of the study area to depths 

 of over 200 feet in Stellwagen Basin. Except in the north where the slope 

 is broken up by submarine hills and ridges the inclined bottom is rela- 

 tively smooth and uniform. 



Slope Dl extends northwestward into the mass of offshore submarine 

 hills and ridges of area C (Fig. 5). The slope descends from a section of 

 bottom with characteristic depths of 110 feet or less to a small section 

 of level bottom with characteristic depths of over 140 feet. It continues 

 for 3.5 nautical miles southeastward from the east margin of the study 

 area (Fig. 4) . 



Slope D2 is a broad, highly irregular incline beginning northeast of 

 Point Allerton at the north end of Nantasket Beach and extending eastward 



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