DISCUSSION OF SEA FLOOR FEATURES 

Introduction

   The Stellwagen Bank National Marine Sanctuary Mapping Project is a cooperative effort of the U.S. Geological Survey and the National Oceanic and Atmospheric Administration, with support from the University of New Brunswick and the Canadian Hydrographic Service. Multibeam echo sounder surveys were conducted on four cruises over a two-year period from the fall of 1994 to the fall of 1996. Results of these cruises are presented here in a series of 18 mapped quadrangles (see location map) in which sea floor depth information is depicted in sun-illuminated (or shaded relief) view at a scale of 1:25,000, with topographic contours overprinted in blue (Valentine and others, 1999a-r). The shaded relief images shown here were created using a light source that is 45 degrees above the horizon from an azimuth of 350 degrees. The vertical exaggeration in the images is four times. In effect, topographic relief is enhanced by illuminating the sea floor from a position 10 degrees west of north so that shadows are cast on the southern flanks of seabed features. Some features in the images are artifacts of data collection. They are especially noticeable where the seabed is smooth and include small highs and lows and unnatural-looking features and patterns that are oriented parallel or perpendicular to survey tracklines. For a depiction of the topographic contours alone, and for an explanation of survey and topographic data processing methods, see the companion maps by Valentine and others (1997a-r). Topographic contour maps of all 18 quadrangles of the map series are available on a CD-ROM in EPS, PS, Arc export, and PDF file formats (Valentine and others, 1998). Blank areas represent places where no data exists.

  Survey methods

    The survey was conducted using a multibeam echo sounder installed aboard the Canadian Hydrographic Service vessel Frederick G. Creed, a SWATH (Small Waterplane Area Twin Hull) ship that surveys at speeds up to 16 knots.   During the survey, the ship's position was determined with an accuracy of 10 m or better using a global positioning system (GPS) receiver in conjunction with differential GPS corrections transmitted by U.S. Coast Guard radio beacons.  The multibeam echosounder data were collected utilizing a Simrad Subsea EM 1000 Multibeam Echo Sounder (95 kHz) that is permanently installed in the hull of the Creed.  In water depths between 5 and 200 m, the EM 1000 generates 60 aimed beams spaced at intervals of 2.5 degrees that insonify a swath of sea floor measuring in width approximately 7.5 times the water depth; horizontal spatial resolution is on the order of 10 percent of the water depth at 16 knots; vertical resolution is approximately 1 percent or better. Software developed by the Ocean Mapping Group, University of New Brunswick, was used to process and edit the echosounder bathymetric and differential GPS navigation data; tidal corrections based on NOAA's Boston tide gauge were used to reference depth data to mean lower low water.

 Topographic contour mapping

    Bathymetric data were contoured using the Arc/Info geographic information system software (Environmental Systems Research Institution, Inc., version 7.03).  Processed data were formatted into a point file using the Arc/Info "point generate" routine. The point file was transformed to a Mercator projection with the longitude of the central meridian at 70^o 19'W and the latitude of true scale at 41^o 39'N.  The "point grid" routine was used to create a grid from the point file and to assign depth values to individual grid cells.  The cell size of the output grid was 13 m.  Topographic contours at 5-meter intervals were generated using the "lattice contour" routine.   Most of the contour lines are displayed here uneditted.   However, in areas of very smooth sea floor, some contours displayed distortions that are due to problems encountered during data acquisition at nadir (directly below the vessel's keel) and to refraction effects at the outermost edge of the swath.  These distortions were smoothed by using a user-defined low-frequency "focal median" filter routine on the grid created by "point grid".  Square focal median filters varying in size from 5 x 5 to 21 x 21 cells were tried, and a 9 x 9 cell size was selected for Quadrangles 1-4 and 6-18; an 11 by 11 cell size was chosen for Quadrangle 5. The resulting contours were compared with features displayed in shaded relief seabed imagery of the same data and edited manually with "Arc/Edit" to remove small artifacts that remained after filtering.  Each of the quadrangles was contoured independently, and contours that extend into adjacent quadrangles were edited manually to match at the boundary.

 Regional Seabed Features

    The major topographic features depicted in the map series were formed by glacial processes. In broad terms, these features are interpreted here to represent a geologic history that developed in several stages. Ice containing rock debris moved across the region, sculpting its surface and depositing sediment to form the large basins, banks, ridges, and valleys. Many other features observed here represent the latter stages of deglaciation. They are the result of processes at work when much of the area was covered by stationary rotting ice, and when at the same time small valley glaciers and ice falls were active in and near areas of high topographic relief. The sea invaded the region formerly occupied by ice, and seabed features were partly eroded and some new sedimentary deposits were formed. Today, the sea floor is modified mainly by strong southwestward-flowing bottom currents caused by storm winds from the northeast. These currents erode sediments from the shallow banks and transport them into the basins. With time, the banks affected by these currents become coarser, as sand and mud are removed and gravel remains; and the western flanks of the banks, and the adjacent basins, are built up by deposits of mud and sand.

Quadrangle 1 Features
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    The northeastern corner of Quadrangle 1 lies in the southwestern part of Stellwagen Basin. The sea floor here is smooth mud that slopes gently eastward through water depths of approximately 55 to 65 m. The seabed in the remainder of the quadrangle is made up of gravel banks and sandy basins in the west that become increasingly covered with mud as water depth increases toward the basin in the east. In the western and west central part of the quadrangle, the seafloor is characterized by southeastward-trending gravel banks that are separated by basins covered with sand and, to a less extent, muddy sand. The orientation of these features parallels the movement of glacial ice. Similar features are present in the adjacent Quadrangle 4 to the north (Valentine and others, 1999d).

    The banks lie at 15 to 30 m water depth and have a relief of 5 to 10 m. Their surfaces are gravel, including elongate boulder piles and ridges that have a relief of up to 5 m. These features resemble eskers (sand and gravel deposited by running water within stationary glacial ice) and end moraines (deposits of rock debris piled up at the forward edges of moving ice). Eskers are present on the bank tops and flanks (42° 8.9'N, 70° 34.4'W; 42° 9.8'N, 70° 35.9'W). Probable end moraines are located on the southeastern ends of the banks and are oriented northeastward, across the regional grain (42° 9.9'N, 70° 34.9'W; 42° 7.8'N, 70° 30.4'W). These gravel features are, in places, partly covered by a thin veneer of sand. Shallow, irregularly-shaped depressions in the sea floor possibly outline the former locations of large masses of melting glacial ice (42° 10.5'N, 70° 33.3'W; 42° 9.8'N, 70° 34.4'W).

    The basins that lie between the gravel banks are covered with sand and gravelly sand. A deep basin (40 m and deeper) has a smooth floor covered with sand (42° 11.6'N, 70° 34.4'W). A basin of intermediate depth (30 to 40 m) is rougher and is floored with coarser sand and gravel (42° 10.9'N, 70° 34.8'W). Shallow basins (20 to 30 m) are covered with bedforms and sand and gravel deposits that are oriented northeastward, across the grain of the bounding gravel banks (42° 7.9'N, 70° 34.6'W).

    In the southwestern corner of the quadrangle, sand deposits in the form of elongated ridges (42° 5.5'N, 70° 34.8'W) and rounded features (42° 5.4'N, 70° 33.5'W) in 20 to 30 m water depth are finer-grained than the sand in adjacent areas of the seabed. The sea floor that lies between the basins and gravel banks of the western part of the quadrangle and the mud basin of the eastern part is characterized by shallow basins and gravel banks of low relief that are partly buried by sand and muddy sand (42° 6.3'N, 70° 27.2'W; 42° 11.0'N, 70° 31.0'W). A low round hill of coarse sediment that is almost covered with mud lies in the northeastern part of the quadrangle at 60 to 65 m water depth (42° 11.8'N, 70° 27.1'W).

    Within the region of partly-buried banks and basins, there are scattered exposures of coarse-grained sand that are partly covered with deposits of fine-grained sand (42° 5.3'N, 70° 30.0'W; 42° 11.4'N, 70° 32.7'W). The edges of the fine layer, where they bound the coarse sand exposures, are curved and sharply defined, as if formed by bottom currents. It is possible that the coarse deposits have been exposed by bottom currents that have eroded the overlying fine layer. Similar features are present in the adjacent Quadrangle 4 to the north.

Quadrangle 2 Features
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    This quadrangle covers the southwestern corner of Stellwagen Bank, the southeastern part of Stellwagen Basin, and the western part of the channel that separates the bank from Cape Cod. The southernmost extremity of the bank, the shallowest part of the bank overall, lies at a water depth of 20 m in the center of the quadrangle and is bounded on the south and southwest by a 25-meter escarpment. The southwestern face of the escarpment bears a prominent notch that incises the bank for approximately one kilometer. The bank crest is relatively flat in water depths of 20 to 30 m. The western flank of the bank slopes from a water depth of 30 m to meet the floor of Stellwagen Basin at 55 m. The seabed between 20 and 40 m is covered by sand and gravelly sand. In this interval, the smooth seabed is relatively uniform in texture, and curved features of low relief represent the intermingling of storm deposits of fine and coarse sand. A wedge-shaped feature in the northern part of the quadrangle (70° 20'W) is part of a storm deposit of fine-grained sand dunes that extends southward from Quadrangle 5 (Valentine and others, 1999e).

    The western flank of the bank extends westward into Stellwagen Basin as a terrace of low relief in the 40- to 50-m depth interval. Its surface is slightly hummocky sand and muddy sand that is interpreted to represent storm deposits. To the west, the basin floor is sandy mud and mud. Several sets of low curved ridges intersect the southern escarpment of the bank. The best-defined ridges are at 45 m water depth and resemble rock debris deposited from the lobe of a former ice fall that flowed from the bank. A better preserved feature of similar origin is present at the base of a small bank located in Quadrangle 6 to the east (Valentine and others, 1999f).

    In the southern part of the quadrangle, in water depths of 50 to less than 65 m, the channel between the bank and Cape Cod opens westward into Stellwagen Basin. The channel floor is sandy and gradually becomes finer-grained and muddy as it merges with the basin to the west. The seabed in this region displays low ridges, grooves, and hummocks that are interpreted to have formed by glacial processes during a time of ice movement and a later time of ice melting. These features are now covered to varying degrees by sediment. They are clearly observed in the deep parts of the channel and in the basin to the west, but they are less visible near the bank margins where they have been more deeply buried by sediment from the bank.

Quadrangle 3 Features
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    This quadrangle covers the southeastern corner of Stellwagen Bank and the eastern part of the channel that separates the bank from Cape Cod to the south. In the northern part of the quadrangle, the bank surface slopes gently eastward through water depths of 30 to 55 m and is covered with coarse gravelly sand. A low scarp (5-10 m) delineates the southern edge of the bank from the channel to the south. The sandy eastern bank edge lies in water depths of 55 to 80 m and extends southeastward to form the eastern threshold of the channel. The northern part of the bank edge is dissected by shallow downslope gullies; the central part is smooth, probably the result of recent sediment deposition; and the southern part is covered by low bedforms oriented oblique to the slope of the seabed.

    The southern half of a poorly-defined bank is located in the northeastern part of the quadrangle. The summit of the bank lies at 90 m water depth and is covered with sand and gravel and a partly-buried gravel ridge. This bank is the southernmost of a series of 90-meter banks that extend from this quadrangle northward into Quadrangle 6 (Valentine and others, 1999f). The smooth valley south and east of the bank is floored with muddy sand.

    The east-west channel that separates Stellwagen Bank and Cape Cod lies in water depths of 45 to 60 m. The shallowest region of the channel floor is coarse-grained sand occurring as ripples and dunes in a discontinuous thin veneer on gravel. The deeper western and eastern parts of the channel floor are finer-grained sand. The channel floor gradually deepens to the west in Quadrangle 2 (Valentine and others, 1999b) where it becomes muddy as it opens into Stellwagen Basin. Three distinct sets of low sand bedforms occur in the southern part of the channel in this quadrangle. In the east (to seaward), elongated dunes oriented along-current and parallel to regional topography extend for 7 km around the northern face of Cape Cod. They merge at 70° 09'W with a western set of dunes that are oriented across-current and perpendicular to regional topography. Both bedform sets are coarse sand, and the change in orientation may reflect a difference in the speeds of storm wave and tidal currents in the channel, with the eastern part experiencing the strongest currents. A third set of bedforms of finer-grained sand has formed in the deeper water (55-60 m) of the southwestern part of the quadrangle. South of the bedform region, between 70° 08'W and 70° 12'W, a smooth apron of coarse sand extends from the northern flank of Cape Cod into the channel.

Quadrangle 4 Features
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    Much of Quadrangle 4 lies in the southeastern part of Stellwagen Basin where the sea floor is relatively smooth mud that slopes northeastward through water depths of 45 to 95 m. Three large elongated banks are present in the basin. They are 4.5 to 6.2 km in length, their tops lie in water depths of 55 to 65 m, and they have a relief of 15 to 30 m. The surfaces of the banks are sand and gravel, including boulder piles and ridges, and a thin veneer of mud. The internal composition of the banks is unknown. Their northwest-southeast elongated shape suggests formation by glacial processes that eroded surrounding less-resistant sediment and rock during ice movement to the southeast and that further modified the banks during later melting of the ice. The bank in the northeast corner of the quadrangle (42° 19.2'N, 70° 26.5'W) also lies partly in the adjacent Quadrangle 7 to the north (Valentine and others, 1999g). It has a subelliptical shape and a relatively flat surface. Another bank is located in the south central part of the quadrangle (42° 15'N, 70° 29'W). It is long and narrow, and its western flank has been eroded into two arcuate embayments. The third bank lies along the eastern edge of the quadrangle (42° 15'N) and is more eroded than the other two; it extends southeastward into the adjacent Quadrangle 5 (Valentine and others, 1999e). A small, low hill, located near the northwestern edge of the quadrangle (42° 17.9'N, 70° 35.4'W), has a relief of only a few meters and possibly is the eroded remnant of a bank. Its surface, at 55 m water depth, is covered with gravel and a veneer of sandy mud.

    West and south of this feature, along the western edge of the quadrangle (42° 16.8' to 42° 18.3'N) at 50 to 55 m, there are scattered exposures of coarse-grained sand that are partly covered with deposits of fine-grained sand. The edges of the fine layer, where they bound the coarse sand exposures, are curved and sharply defined, as if formed by bottom currents. It is possible that the coarse deposits have been exposed by bottom currents that have eroded the overlying fine layer. Similar features are present in the adjacent Quadrangle 1 to the south (Valentine and others, 1999a).

    The southwestern part of the quadrangle is a complex of long, southeastward-trending gravel banks that are separated by elongate basins covered with sand and muddy sand. The orientation of these features parallels the movement of glacial ice. Similar features are present in Quadrangle 1. The banks lie at 30 to 35 m water depth and have a relief of 5 to 10 m. Their surfaces are gravel, including elongate boulder piles and ridges that have a relief of less than 5 m. These features resemble eskers (sand and gravel deposited by running water within stationary glacial ice) and end moraines (deposits of rock debris piled up at the forward edges of moving ice). Eskers are present on the bank tops and flanks (42° 15.3'N, 70° 34.7'W) and probable end moraines are located on the southeastern ends of the banks and are oriented northeastward, across the regional grain (42° 13.3'N, 70° 32.1'W; 42° 12.2'N, 70° 32.7'W). These gravel features are, in places, partly covered by a thin veneer of sand. Shallow, irregularly-shaped depressions in the sea floor outline the former locations of large masses of melting glacial ice (42° 14.3'N, 70° 33.3'W).

    The basins that lie between the gravel banks are covered with sand and gravelly sand. The sand deposits that cover the southwestern flanks of two ridges (42° 12.6'N, 70° 33.1'W; 42° 13.0'N, 70° 35.0'W) display southwest-trending grooves that are interpreted to have been caused by the gouging of icebergs that drifted southwestward from ice located on the banks. The grooves are up to 50 m wide and 1.5 km long and are less than 5 m deep. They do not appear at water depths greater than 35 to 40m.

    A large lobe of sediment (42° 13'N, 70° 30'W) extends eastward into the basin. This feature has a relief of several meters along its southern margin, and its surface varies from muddy sand in the west to sandy mud with increasing water depth to the east. In one area of the basin, the smooth, almost flat mud floor is interrupted by a shallow depression that is irregular in outline and surrounds small mounds (42° 17.3'N, 70° 34.5'W). The depression is 600 m long. Observations in Quadrangles 7 and 8 (Valentine and others 1999g, h) have shown similar mounds to be patches of gravel, including boulders, that are frequented by groundfish. Some boulders and smaller gravel are exposed in the bottom of pits in the mud in which fish are present. The depressions are interpreted to have formed by the scouring actions of groundfish that have exposed the gravel habitat and prevent its burial by basin mud.

Quadrangle 5 Features
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    This quadrangle covers the western central part of Stellwagen Bank and an embayment of Stellwagen Basin into the western flank of the bank. The bank surface slopes eastward and westward from a broad central crest delineated by the 25- and 30-meter contours. Eastward of the crest, extending to a depth of 40 m, the gently-sloping sea floor is sand and gravel, including boulder piles and ridges. The central bank crest and western flank are somewhat finer-grained sand and gravelly sand to a depth of 65 m. Both the eastern and western flanks exhibit a variety of sand deposits and bedforms that indicate movement of sand from northeast to southwest by storm wave currents. These deposits typically are a series of coarse and fine sand bodies that have segregated during transport. In the northeastern part of the quadrangle, the deposits are long and linear and trend northwest; they surround three large parallel boulder ridges with relief of several meters (42° 18'N, 70° 17'W) that trend northeast. On the bank crest, in the southeastern part of the quadrangle, migrating sediment has been formed into rounded deposits of varying textures. On the western flank of the bank, sand becomes gradually finer-grained with increasing water depth; but in some areas, the seabed is composed of large sheets of fine-grained sand waves interfingering with and overlying coarse sand (lower central part of the quadrangle, along 70° 19'W).

    The western flank gives way at 70 to 75 m to the smooth muddy floor of Stellwagen Basin. In several areas of the basin, the almost flat sea floor is interrupted by shallow irregular depressions that surround low mounds and that are similar to features observed in Quadrangles 7 and 8 (Valentine and others, 1999g, h). The features range up to several hundreds of meters in length (42° 15.0'N, 70° 22.0'W; 42° 17.6'N, 70° 20.9'W). Observations have shown the mounds to be patches of gravel, including boulders, that are frequented by groundfish. Some boulders and smaller gravel are exposed in the bottoms of pits in the mud in which fish are present. The depressions are interpreted to have formed by the scouring actions of groundfish that have exposed the gravel habitat and prevent its burial by basin mud.

    Two spurs extend northwestward from the bank into Stellwagen Basin. The southernmost spur is a rough-surfaced low boulder ridge, partly buried by muddy sand, and a connected bank of low relief that extends into Quadrangle 4 (Valentine and others, 1999d). The northernmost spur and an adjacent small bank lie at 65 m and 70 m, respectively, and have a relief of 25 to 30 m. Their surfaces are dominantly sand and gravel, including boulders. The surface of this spur exhibits several irregular depressions that possibly outline the former locations of large masses of melting glacial ice. Together, the spur and small bank extend northwestward into the basin and are alined with three elongate banks located in Quadrangles 4 and 7 (Valentine and others, 1999d, g). The surfaces of the banks are sand and gravel, including boulder piles and ridges, with a thin veneer of mud. The internal composition of the banks and spur are unknown. Their elongate shape suggests formation by glacial processes, chiefly by erosion of surrounding less-resistant sediment and rock. The northernmost spur in this quadrangle resembles a bank that has partly emerged from Stellwagen Bank proper through erosion of the surrounding rock materials by glacial ice.

Quadrangle 6 Features
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    This quadrangle covers the eastern central part of Stellwagen Bank and several banks that lie to the east. The bank surface slopes gently eastward through water depths of 35 to 75 m and is covered with sand and gravel. In the 50- to 75-meter interval, the surface is very rough due to the presence of large depressions and boulder piles and ridges. Many of the boulder ridges resemble eskers (sand and gravel deposited by running water within stationary glacial ice). The ridges commonly are constructed of boulders and cobbles that are now separated by voids from which sand and small gravel presumably were eroded during advance of the sea after the glacial ice melted. The shallow depressions in the sea floor (42° 16.8'N, 70° 09.3'W) possibly outline the former locations of large masses of melting glacial ice. The bank margin is formed by the walls of valleys that extend into deeper water to the east. In the north central part of the quadrangle, the bank edge is capped by a linear north-trending sand bank, that extends into Quadrangle 9 (Valentine and others, 1999i) and is dissected by shallow southeast-trending gullies. The sand bank lies in water depths of 70 to 75 m and is surmounted by arcuate ridges 5 m high that display bedforms on their surfaces.

    Three prominent flat-topped banks lie at depths of 90 to 95 m in the eastern part of the quadrangle. The bank tops are sandy and gravelly and display shallow depressions and boulder ridges that are similar to features on Stellwagn Bank described above. The northern part of a fourth 90-meter bank lies on the southeastern edge of the quadrangle and extends into Quadrangle 3 (Valentine and others, 1999c). It is less well formed than the others, and its surface of sand and gravel is less rough. The banks are separated from Stellwagen Bank and from each other by shallow, smooth-floored valleys that appear to have been deepened by the movement of small glaciers.

    The valley floors are muddy sand. The valley walls exhibit narrow ridges that parallel topography and are interpreted to be lateral moraines (deposits of rock debris piled up at the edges of moving ice) now covered by muddy sand. A rough-surfaced lobate feature of low relief extends from the base of the southern flank of the easternmost bank (42° 15.7'N). It is interpreted to be rock debris deposited from the lobe of an ice fall that flowed from the top of the bank into the valley below. It retains its distinctive shape beneath a thin layer of muddy sand. A feature of similar origin lies across the valley at the base of the opposing bank to the south (42° 15.1'N). Hummocky topography in the northeastern corner of the quadrangle represents the eroded western flank of another 90-meter bank whose summit lies 800 meters east of the quadrangle boundary.

Quadrangle 7 Features
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    This quadrangle covers the northwestern end of Stellwagen Bank and the central part of Stellwagen Basin. The bank crest is relatively flat in water depths of 30 to 35 m where it is covered with sand and gravelly sand. A sheet of fine-grained sand caps the northern edge of the bank. The eastern part of the bank's northern flank slopes steeply through water depths of 40 to 90 m to form the head of a north-trending glacial valley that extends into Quadrangle 10 (Valentine and others, 1999j). The valley head is covered with sand, becoming finer-grained with depth. The western part of the bank's northern flank slopes less steeply to a depth of 50 m to meet the nearly flat surface of a broad terrace that extends the bank northwestward. Sand transported from the bank covers the southeastern part of the terrace, where the surface is smooth except for shallow gullies on the eastern slope.

    Both Stellwagen Bank and the terrace are separated from Stellwagen Basin to the southwest by a continuous northwest-trending escarpment that is 40 m high along the bank edge and is reduced to 25 m along the terrace edge. The terrace surface is smooth along its southwestern edge, where it is covered with gravelly sand and gravel; to the north, it is covered with gravel, including boulder piles and ridges, and displays irregularly-shaped depressions that possibly outline the former locations of large masses of melting glacial ice. A band of irregular seabed at the base of the escarpment that is characterized by low mounds and ridges and by shallow depressions is interpreted to be glacial debris deposited by ice that flowed off the terrace. Some of the roughness of these features has been smoothed by a veneer of mud.

    Stellwagen Basin occupies the central and southern part of the quadrangle. The basin floor ranges in depth from 70 to 95 meters, is covered by mud, and is relatively smooth except where it is interrupted by several kinds of topographic highs and some small shallow depressions. The most prominent basin features are three large elongated banks that lie in the southern part of the quadrangle. They are part of a group of four banks that extends southeastward into Quadrangle 4 and are alined with the large spur on the western margin of Stellwagen Bank in Quadrangle 5 (Valentine and others, 1999d, e). The three banks in this quadrangle are 3.7 to 6.3 km in length, their tops lie in water depths of 55 to 65 m, and they have a relief of 25 m. The bank surfaces are sand and gravel, including boulder piles and ridges, and a thin veneer of mud.

    The internal composition of the banks is unknown. Their northwest-southeast elongated shape (and the deep grooves and pits on two of the banks) suggests formation by glacial processes that eroded surrounding less-resistant sediment and rock during ice movement to the southeast and further modified the banks during later melting of the ice. The surfaces and perimeters of the two westernmost banks are more irregular (eroded) than the surfaces of the other bank in this quadrangle (and in Quadrangle 4) and of the similarly-alined spur in Quadrangle 5. This suggests that either the banks differ in composition or the southeasternmost banks are younger. The shapes of the banks might represent an evolutionary progression (as a result of ice movement toward the southeast) of bank formation followed by destructive erosion.

    A large, broad, hummocky mound is located north of the banks. Its surface is sand and gravel, including boulder piles, and a veneer of mud. The tops of the boulder piles are at 60 m water depth, and the relief of the mound is 25 to 30 m. This feature is interpreted to be a former bank in a later stage of erosion than the grouping of banks that lie to the south of it. In addition to large banks that apparently are erosional in origin, the basin floor displays features that might be depositional in origin. Among these are small pear-shaped mounds that have a length of 375 to 900 m and a relief of 10 to 20 m. They are rounded and streamlined in a northwest-southeast direction and are interpreted to be drumlins composed of glacial sediment that were formed during ice movement (42° 21.3'N, 70° 30.6'W; 42° 22.7'N, 70° 30.0'W; 42° 23.6'N, 70° 34.1'W; and at 42° 26.3'N, 70° 34.9'W).

    The Massachusetts Bay Disposal Site lies in the northwest corner of the quadrangle, west of the sanctuary boundary (see detailed maps of the disposal site by Valentine and others, 1996, 1999s). A rough-surfaced mound of disposed dredged material 6 to 7m in height is present at the active disposal point (42° 25.1'N, 70° 34.5'W). Hummocky deposits of disposed rock debris are present on the edge of the terrace along the northern edge of the quadrangle (70° 34'W).

    In several areas of the basin, the smooth, almost flat mud floor is interrupted by shallow depressions. The larger depressions are irregular in outline and surround small mounds, and smaller depressions are elliptical moats that surround a central mound. The depressions range up to several hundreds of meters in length, and observations have shown the mounds to be patches of gravel, including boulders, that are frequented by groundfish. Some boulders and smaller gravel are exposed in the bottoms of pits in the mud in which fish are present. The depressions are interpreted to have formed by the scouring actions of groundfish that have exposed the gravel habitat and prevent its burial by basin mud. Representative scour depressions are present in areas centered on 42° 21.5'N, 70° 26.0'W, and on 42° 21.1'N, 70° 29.2'W.

Quadrangle 8 Features
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    This quadrangle covers the north central part of Stellwagen Bank, part of the northeastern flank of the bank, and an embayment of Stellwagen Basin into the western flank of the bank. The bank crest is relatively flat and lies at a water depth of less than 30 meters where it is covered with sand and gravelly sand. The bank slopes gently northeastward through water depths of 35 to 70 m. From 35 to 50 m it is covered with sand and gravel, including some boulder piles and ridges. In the 50- to 70-meter interval, the surface generally is very rough due to the presence of boulder ridges and some depressions. The depressions possibly outline the former locations of masses of melting glacial ice. In the east central part of the quadrangle, the northeastern flank, at depths of 60 m and shallower, exhibits a variety of sand deposits and bedforms that indicate movement of sand from northeast to southwest by storm wave currents. These deposits are a series of coarse- and fine-grained sand bodies that have segregated during transport. In much of the area, the deposits are long and linear and trend northwest.

    In the southern part of the quadrangle, parallel boulder ridges having a relief of several meters (42° 20.5'N, 70° 17.5'W), trend northeast and temporarily anchor migrating deposits of coarse and fine sand. Similar boulder ridges are present on the bank crest to the south in Quadrangle 5 (Valentine and others, 1999e). In the northwestern corner of the quadrangle at water depths of 35 to 50 m, the bank margin is capped by a sand sheet. The bank=s northern flank slopes steeply through water depths of 50 to 90 m to form the eastern part of the head of a north-trending glacial valley that extends into Quadrangles 7, 10, and 11 (Valentine and others 1999g, j, k). The valley head is covered with fine-grained sand that becomes muddy with depth. The head of an adjacent, parallel valley to the east incises the northern flank at 70° 21'W in water depths of 65 to 80 m and extends northward into Quadrangle 11.

    The bank is separated from Stellwagen Basin to the southwest by a northwest-trending escarpment that varies from 20 to 30 m in height. The bank edge is sand and gravelly sand except where it is armored by a gravel pavement in the area lying between 42° 21'N and 42° 22'N. A band of irregular seabed along the base of the escarpment (north of 42° 21'N) that is characterized by small mounds and depressions is interpreted to be glacial debris deposited by ice that flowed off the bank. This deposit is lightly veneered with mud in its southeastern part; but to the northwest, and extending into Quadrangle 7 (Valentine and others 1999g), it is covered with sand and mud that has been transported off the bank. The foot of the escarpment in the southern part of the quadrangle is marked by a narrow ridge that parallels topography and is interpreted to be a lateral moraine (deposit of rock debris piled up at the edge of moving ice) now covered by muddy sand.

    The relatively smooth basin floor ranges in depth from 75 to 105 m; it is covered with muddy sand below the bank escarpment and with mud farther west. The southern margin of the basin here is bounded by a spur of Stellwagen Bank and a small adjacent bank that have a relief of 25 to 30 m and are covered with sand and gravel, including boulders (see adjacent Quadrangle 5 map; Valentine and others, 1999e). On the western edge of the quadrangle, between 42° 21'N and 42° 22'N, the smooth, almost flat mud floor is interrupted by shallow irregular depressions and low mounds that lie near similar features in Quadrangle 7 to the west (Valentine and others, 1999g). These features range up to several hundreds of meters in length, and observations have shown the mounds to be patches of gravel, including boulders, that are frequented by groundfish. Some boulders and smaller gravel are exposed in the bottoms of pits in the mud in which fish are present. The depressions are interpreted to have formed by the scouring actions of groundfish that have exposed the gravel habitat and prevent its burial by basin mud.

Quadrangle 9 Features
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    This quadrangle covers the northeastern flank of Stellwagen Bank. The bank surface slopes gently northeastward through water depths of 50 to 100 m and is covered with sand and gravel. In the central and eastern parts of the quadrangle, the gravelly sea floor is very rough due to the presence of boulder piles and ridges and large depressions. Many of the boulder ridges resemble eskers (sand and gravel deposited by running water within stationary glacial ice). Other prominent boulder ridges are located along the upper margins of small valleys (42° 21.4'N, 70° 04.1' W). They appear to be lateral moraines (deposits of rock debris piled up at the edges of moving ice) formed by small valley glaciers. The boulder ridges commonly are constructed of boulders and cobbles that now are separated by voids from which sand and small gravel presumably were eroded during advance of the sea after the glacial ice melted. The depressions (42° 20.5'N, 70° 08.5'W) possibly outline the former locations of large masses of melting glacial ice.

    Several large coarse-grained sand deposits are present in this quadrangle. In the northwestern part, the sea floor is dominated by a northeast-trending sand bank that lies at 70 m and is imprinted with northwest-trending gullies and bedforms. In the east central part, a series of northeast-trending sand banks (interrupted by a deep narrow valley at 42° 23'N) are present at depths of 75 to 85 m; these features are part of a larger system of sand banks that extends southwestward into Quadrangle 6 (Valentine and others, 1999f). In the southeastern corner of Quadrangle 9, the bank edge is capped at 85 m by linear sand banks below which sediment becomes finer-grained and muddy with increasing water depth. Hummocky topography in the southeastern corner of the quadrangle in water depths of 130 to 180 m represents buried rock debris and the eroded western flank of a 90-meter bank whose summit lies 900 meters southeast of the quadrangle corner.

    The bank margin here displays multiple narrow ridges that parallel topography and are interpreted to be lateral moraines. These are deposits of rock debris, now covered with muddy sand, that were piled up at the edge of moving ice that flowed northeastward down a valley that begins in Quadrangle 6 to the south (Valentine and others, 1999f). Another lateral moraine partly buried by sand is present in the northeast corner of Quadrangle 9. The seabed to the east of this feature is muddy sand and displays northeast-trending grooves caused by the gouging of icebergs that grounded here during the late stages of the last glaciation. The grooves are approximately 5 m deep and up to 100 m wide.

    The floor of a shallow valley at 42° 24'N on the eastern edge of this quadrangle displays low gravelly ridges whose distinctive mesh-like pattern resembles that of crevasse fills (sediment deposited in large cracks in glacial ice). Similar patterns are present near the northern edge of the quadrangle between 70° 09'W and 70° 10'W and in the adjacent Quadrangle 12 to the north (Valentine and others, 1999l). Short, dark angled lines located along 42° 20'N latitude are not features but are artifacts in the sonar records that mark the ends of survey lines.

Quadrangle 10 Features
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    The northeastern part of Quadrangle 10 is a smooth muddy sea floor that slopes northeastward through water depths of 80 to 120 m. It is part of a large basin that extends into Quadrangles 11 and 13 (Valentine and others, 1999k, m). A small part of a flat-topped bank (42° 33.0'N, 70° 24.8'W) is present along the northeastern edge of Quadrangle 10. At the base of this bank are hummocky, lobe-shaped features that extend into the basin. They are interpreted to have been formed by glacial debris (now covered with sandy mud) that was deposited by ice falls that flowed from the bank above. The smooth basin floor is interrupted by two small, elongate banks (42° 32.0'N, 70° 25.4'W; 42° 31.2'N, 70° 24.7'W). They are part of a southeastward alinement of small banks that extend into Quadrangle 11 and reflect the direction of movement of glacial ice in the basin.

    Most of the rest of Quadrangle 10, north of approximately 42° 29'N, is a complex of flat-topped banks and rounded hills of varying sizes that are separated by the relatively smooth seabed of small basins and valleys. The surfaces of the positive features lie at 45 to 75 m water depth and are gravel that in places is covered with a thin veneer of sand. The elongated, rounded features resemble drumlins and drumlinoid ridges characteristic of glaciated terrain, and their northeastern trend suggests the direction of ice movement in this area. The banks are modified by small valleys and basins, and by boulder piles and ridges that have a relief of up to 5 m and are interpreted to be lateral moraines (deposits of rock debris piled up at the edges of moving ice) and eskers (sand and gravel deposited by running water within stationary glacial ice).

    Lateral moraines are present along many of the upper margins of small valleys (42° 30.4'N, 70° 33.6'W; 42° 29.6'N, 70° 28.8'W). Eskers are common on the bank tops and are present as solitary features (42° 29.5'N, 70° 28.2'W) and as networks of sinuous sharp gravel ridges (42° 33.3'N, 70° 32.8'W). The boulder piles and ridges commonly are constructed of boulders and cobbles that are now separated by voids from which sand and small gravel presumably were eroded during advance of the sea after the glacial ice melted. The seabed in the small basins and valleys on the banks and around the margins of the banks and hills is muddy sand; the deep parts of the small basins and valleys that separate the banks are sandy mud.

    A deep valley floored with sandy mud is present in the southeastern corner of the quadrangle. It extends northwestward through water depths of 85 to 105 m and turns northward to form a narrow basin (42° 29.5'N, 70° 27.2'W) bounded by two banks whose steep flanks have a relief of 60 m. The basin floor reaches a depth of 125 m and its hummocky surface possibly represents gravelly debris (now covered with muddy sand) that was transported by glacial ice. A low ridge across the valley floor (42° 28.7'N, 70° 27.2'W) resembles an end moraine deposited by the forward edge of glacial ice that occupied the southern part of the valley. The large bank located along the southeastern edge of the quadrangle is dissected by valleys (42° 27.8'N, 70° 25.4'W) that lie partly in the adjacent Quadrangle 11 to the east. The valley floors are muddy sand, and the bank surface is covered with gravel, including boulder piles and ridges. The gravel is covered in places with a thin veneer of sand that is more extensive on the hillsides and in the shallow depressions on the bank surface than on the hilltops.

    The southern part of the quadrangle is occupied by the northern part of a large, relatively flat bank that lies at a water depth of 50 to 60 m. The bank=s surface is gravel, including scattered boulder piles and ridges, that represent eskers for the most part. Shallow, irregularly-shaped depressions in the sea floor (42° 27.4'N, 70° 28.8'W), in association with gravel ridges, possibly represent the former locations of large masses of melting glacial ice. The bank margin is incised by shallow valleys whose floors are covered with muddy sand. However, a small basin in the interior of the bank is covered with sandy mud (42° 28.3'N, 70° 30.7'W). Sand with a gullied surface covers the flank of a valley (42° 29.0'N, 70° 30.8'W) in the northern part of the bank. A sand deposit also is present on the southeasternmost part of the bank (42° 26.8'N, 70° 27.4'W). The sand exhibits shallow downslope gullies, and it has been transported here from the northern edge of Stellwagen Bank that lies at a higher level to the south in the adjacent Quadrangle 7 (Valentine and others, 1999g).

    In the western part of Quadrangle 10, the surface of the gravel bank is separated from a deep muddy basin to the west by a northwestward-trending escarpment 30 m high. The basin floor slopes northward from 85 m at the foot of the bank to 105 m in a small basin (42° 28.0'N, 70° 35.6'W) at the mouth of a valley that incises the bank edge. A small drumlin that trends southeastward is present in the southwestern corner of the quadrangle.

    In the deep basin along the western edge of the quadrangle, the smooth, almost flat, mud seabed is interrupted by shallow depressions that are elliptical moats that surround a central mound. The depressions range up to several hundred meters in length, and observations of similar features in Quadrangles 7 and 8 (Valentine and others, 1999g, h) have shown the mounds to be patches of gravel, including boulders, that are frequented by groundfish. Some boulders and smaller gravel are exposed in the bottoms of pits in the mud in which fish are present. The depressions are interpreted to have formed by the scouring actions of groundfish that have exposed the gravel habitat and prevent its burial by basin mud.

Quadrangle 11 Features
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    Quadrangle 11 covers the northern part of Stellwagen Bank (60 to 75 m water depth) and a topographically varied region to the north of the bank that is characterized by banks and complex ridges (60 to 90 m) separated by deep valleys and basins (125 to 180 m). In the southern part of the quadrangle, Stellwagen Bank is relatively flat except where it is incised by northward-trending glaciated valleys. The bank surface here is chiefly gravel and includes boulder piles and ridges. Some of these linear ridges resemble eskers (sand and gravel deposited by running water in channels within stationary glacial ice) and are located along the southern margin (70° 19'W) and in the southeastern corner of the quadrangle. Other ridges are located along the upper edges of both shallow and deep glaciated valleys in the southwestern part of the quadrangle and are interpreted to be lateral moraines (deposits of rock debris piled up at the edges of moving ice).

    The northern flank of the bank and the shallow valleys in the southwestern part of the quadrangle are sandy, becoming muddy with increasing depth into the basin to the north. Sand deposits that display east-west-trending bedforms are located along the northern flank between 70° 17'W and 70° 19'W and between 70° 21'W and 70° 22'W. Broad depressions in the seabed along the eastern margin of the quadrangle, extending from the southeastern corner to 42° 30'N, possibly indicate the former locations of large masses of melting ice. The sea floor here is chiefly gravel, in places partly covered by a thin veneer of sand. Two deep valleys that incise the bank in the southwestern part of the quadrangle are floored with muddy sand. The floor of one valley (70° 21'W) is smooth to a depth of 115 m, from where it displays low ridges and mounds that clog the valley as it proceeds northward into a large basin (42° 29.4'N, 70° 22.6'W). The ridges and mounds possibly represent deposits of gravelly glacial debris transported by ice flows down the steep west wall of the valley. These deposits now are covered with muddy sand. The other valley (70° 24.5'W) is shorter and has a relatively smooth floor.

    The rugged topography of the central and northern parts of the quadrangle displays a regional southeast-trending grain imposed by the direction of movement of a glacial ice sheet. Deep southeast-trending basins separate the banks and ridges. The relatively smooth basin floors are interrupted in some places by small elongate banks (42° 30.4'N, 70° 23.9'W and 42° 32.5'N, 70° 18.9'W) that are alined with the basins. This regional grain has been modified during the late stages of the last glaciation by the movement of small valley glaciers and ice falls and by the melting of masses of stationary ice. Resulting topographic features include well-defined banks with steep flanks and flat tops, and complex ridges, also with relatively steep flanks, but whose surfaces have been dissected by erosion into many small valleys and rounded hills.

    The flat-topped banks ( 42° 33'N, 70° 24'W and 42° 29.7'N, 70° 17.7'W) are covered with sandy gravel and gravel, including boulder piles and ridges. Many hummocky, lobe-shaped depositional features extend from the bases of banks and ridges into the adjacent valleys and basins. They are interpreted to have been formed by glacial debris (now covered by muddy sand) that was deposited by ice falls that flowed from the elevated surfaces of the banks and ridges. Several good examples of ice fall deposits lie on the perimeter of a large bank in the northwestern corner of the quadrangle (42° 33'N, 70° 24'W).

    Two complex ridges trend southward from the northern margin of the quadrangle (70° 17'W and 70° 21'W) and display a wide range of topographic features (hills, valleys, and small basins) and related sediment types. Generally, hills are covered with gravel, valleys are sandy, and small basins are muddy sand. The floors of the large basins in this quadrangle are covered with mud that becomes sandy near the perimeters of banks and ridges.

Quadrangle 12 Features
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    This quadrangle covers the deep part of the northeastern flank of Stellwagen Bank. The bank surface is uneven and displays a variety of sediment types and features, but the regional slope is northeastward through water depths of 70 to 140 m. Some of the seabed features extend into this quadrangle from Quadrangle 9 to the south (Valentine and others, 1999i). Much of the quadrangle is characterized by rounded hills of low relief (5-10 m), but some shallow depressions in the sea floor (42° 27.5'N, 70° 12.7'W) possibly outline the former locations of large masses of melting glacial ice. The seabed is chiefly gravel, including boulder piles and ridges. In some places, the gravel is partly covered with a discontinuous thin veneer of sand.

    The sea floor in the northeastern part of the quadrangle exhibits a highly grooved surface. The grooves are approximately 5 m deep and up to 100 m wide and have primarily a northeast-southwest orientation. They are interpreted to have formed by the plowing action of grounded icebergs during the late stages of the last glaciation. In the north central part of the quadrangle, the low elongated and rounded mounds resemble drumlinoid ridges characteristic of glaciated terrain. The surfaces of many of the hills display elongate, sinuous boulder ridges that resemble eskers (sand and gravel deposited by running water within stationary glacial ice). The eskers are common in the south central part of the quadrangle. Other prominent boulder ridges are located along the upper margins of small valleys (42° 31'N, 70° 11'W). They appear to be lateral moraines (deposits of rock debris piled up at the edges of moving ice) formed by small valley glaciers. The boulder ridges commonly are constructed of boulders and cobbles that now are separated by voids from which sand and small gravel presumably were eroded during advance of the sea after the glacial ice melted.

    Three glaciated valleys converge near the center of the quadrangle (42° 31'N, 70° 09'W). They are 20 to 25 m deep and are floored with slightly muddy sand. Mounds of glacial debris are present at the intersection of the valleys. The north-trending valley displays a low transverse ridge (42° 29.2'N, 70° 09.41'W) that may represent a moraine deposited at the northern terminus of a small valley glacier that occupied the southern part of the valley.

    Two glaciated valleys intersect in the northwest corner of the quadrangle. They have a relief of 30 to 40 m and are floored with slightly muddy sand. One valley trends northwest and then bends to the southwest and continues into a deep basin in Quadrangle 11 (Valentine and others, 1999k). The floor of this valley displays a small basin where it intersects with a south-trending hanging valley whose floor is shallower by approximately 5 m (42° 33.2'N, 70° 13.1'W).

    The floor of a shallow valley near the southern margin of the quadrangle (42° 27.5'N, 70° 08.2'W) displays low gravelly ridges whose distinctive mesh-like pattern resembles that of crevasse fills (sediment deposited in large cracks in glacial ice). Somewhat similar patterns are present near the head of a glaciated valley (42° 28.5'N, 70° 09.5'W) and in the adjacent Quadrangle 9 to the south (Valentine and others, 1998b). Two large sand features are present in this quadrangle.

    A large northeast-trending sand bank extends into the southwestern part of the quadrangle from Quadrangle 9 to the south. The bank is imprinted by northwest-trending gullies and bedforms. A long low sand bank, also trending northeastward, lies along the western margin of a shallow valley whose head is located at the southern margin of the quadrangle ( 70° 06'W). The valley separates elevated areas topped by boulder ridges (eskers), and its floor displays low ridges that possibly are crevasse fills.

Quadrangle 13 Features
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    The northeastern corner of this quadrangle is occupied by the southern end of a large bank that extends northeastward through Quadrangle 17 (Valentine and others, 1999q). The bank lies at a water depth of 40 to 50 m, and its surface is mainly gravel that includes boulder piles and ridges. A long rounded ridge that is less than 5 m high and is outlined by the 40 m depth contour trends northeastward for 5.5 km to the eastern edge of the quadrangle. South of this ridge, several other smaller ridges also trend northeastward along the bank (42° 39.7'N, 70° 27.2'W). These parallel ridges possibly represent a recessional series of end moraines (rock debris deposited at the forward edge of glacial ice). The large ridge at 40 m water depth is poorly developed where smaller gravel ridges that trend southeastward are superimposed on it (42° 40.3'N, 70° 26.0'W). The small ridges resemble eskers (sand and gravel deposited by running water within stationary glacial ice). North of the ridge at 40 m, the sea floor is a complex of gravel ridges (eskers and moraines) associated with large shallow depressions that possibly mark the former locations of masses of melting glacial ice (42° 40.7'N, 70° 26.5'W).

    A steep scarp of varying height (15 to 60 m) delineates the bank from adjacent basins and banks that lie to the east and south. The southeastern edge of the bank is capped by a sand deposit that is, in part, elevated above the gravel surface immediately to the north. At the base of the bank=s southeastern margin, there is an apron of sand that has been transported onto the gravelly surface of the deeper adjacent bank (60-75 m). South of the sand apron, the slightly undulating surface of the lower bank is gravel that is partly covered with sand that is most extensive in low areas.

    The southwestern end of the bank is separated by a 30 to 60 m scarp from an eastward-trending valley; and sand transported from the bank covers the northern flank of this valley. The western edge of the bank is a well-defined sinuous scarp with 30 m of relief that extends from water depths of 45 to 70 m to meet the nearly flat surface of a basin. A hummocky feature of low relief extends into the basin from the base of the scarp (42° 40.3'N, 70° 29.2'W). It is interpreted to have been formed by glacial rock debris (now covered in part with sand) that was deposited by an ice fall that flowed from the bank surface above.

    Outcrops of bedrock are present in the northwestern part of the quadrangle. They are extensions of rocks exposed on the nearby islands and coast. A large basin in the northern part of the quadrangle is bounded by these bedrock outcrops and the bank to the east. The basin floor slopes eastward and ranges in depth from 25 to 85 m. It is relatively smooth and is covered with mud except where sandy mud is present along its margins near the bedrock outcrops and the bank. Several rounded hills on the basin floor (42° 39.0'N, 70° 31.4'W) are gravel partly covered with a veneer of mud.

    South of approximately 42° 38'N, the quadrangle is a complex of banks and rounded hills that lie at 45 to 75 m water depth and that are surrounded by a relatively smooth seabed that slopes eastward to form several valleys in the eastern part of the quadrangle. The banks and hills are elongate, low (5 to 20 m of relief) and are rounded in outline. They range from 400 m to 5.5 km in length. Their surfaces are gravel, including boulder piles and ridges; and the gravel is covered in places with a thin veneer of sand that is most extensive on the hillsides. These features resemble drumlins and drumlinoid ridges composed of glacial debris that were formed by deposition during ice movement.

    The surfaces of some of these features are covered with networks of sinuous sharp gravel ridges (42° 34.2'N, 70° 32.2'W; 42° 35.3'N, 70° 33.0'W) that are interpreted to be eskers (sand and gravel deposited by running water within stationary glacial ice). The ridges commonly are constructed of boulders and cobbles that are now separated by voids from which sand and small gravel presumably were eroded during advance of the sea after the glacial ice melted.

    A triangular bank is present (42° 35.5'N, 70° 26.5'W) in the southeastern part of the quadrangle. Its surface is rounded hills of gravel separated by shallow depressions and small valleys. The gravel hills are covered in part by a thin veneer of sand that is more common on hillsides that on hilltops, and the depressions are covered with sand. This bank is bounded on the north and east by a valley that extends eastward through water depths of 85 to 135 m and then continues southward along the eastern side of the bank to a depth of 145 m. The valley floor is covered with sandy mud, the sand having been transported into the valley from the bounding banks. Within the valley, at the base of the north wall (42° 36.8'N, 70° 25.0'W), a hummocky feature of low relief is interpreted to be rock debris deposited by an ice fall that flowed from the bank above. This feature lies partly in Quadrangle 14 to the east (Valentine and others, 1999n). Smaller features of similar origin lie along the base of the south wall of the valley (42° 36.2'N, 70° 24.9'W; 42° 35.5'N, 70° 24.9'W).

    Two parallel valleys (42° 34'N, 70° 29'W; 42° 35'N, 70° 28'W) are present south of the triangular bank. Their smooth floors are covered with sandy mud and extend from 85 to 90 m water depth southeastward to approximately 105 m at the southern edge of this quadrangle. On the banks in the southern part of the quadrangle, narrow grooves in the seabed that typically are up to 50 m wide, less than 5 m deep, and up to a kilometer long, are interpreted to be marks make by the jagged bottoms of icebergs that gouged the seabed by grounding here during the late stages of the last glaciation. They are present at 70 to 85 m water depth. Similar grooves are also present in the adjacent Quadrangle 14 to the east.

    In several areas of the basin, the smooth mud seabed is interrupted by shallow depressions (42° 34.9'N, 70° 30.6'W; 42° 35.2'N, 70° 29.2'W; 42° 36.26'N, 70° 32.65'W). The depressions are irregular in outline and up to several hundreds of meters in length, and some of them surround small mounds. Observations of similar features in Quadrangles 7 and 8 (Valentine and others, 1999g, h) have shown them to be patches of gravel, including boulders, that are frequented by groundfish. The depressions in the mud are interpreted to have formed by the scouring actions of groundfish that have exposed the gravel habitat and prevent its burial by basin mud. The long, narrow, evenly-spaced stripes displayed in the sea floor image (they trend northeastward on the large bank and in other directions elsewhere in the quadrangle) are artifacts of the survey and do no represent seabed features.

Quadrangle 14 Features
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    The sea floor in Quadrangle 14 is topographically variable and includes banks, shallow and deep basins and valleys. The southeastern part of a shallow bank named Jeffreys Ledge is located in the far northwestern corner of the quadrangle. The seabed of Jeffreys Ledge at water depths of 35 to 50 m is gravel and includes boulder piles and ridges and a large depression (42° 40.3'N, 70° 24.6'W) that possibly marks the former location of a mass of melting ice. Sand and shell deposits cap the edge of Jeffreys Ledge from a depth of 50 m to the base of the bank at 65-70 m, where an adjacent deposit of sand extends southward (42° 38.3'N, 70° 24.4'W).

    A broad bank that dominates the western part of the quadrangle slopes gently southward from Jeffreys Ledge through water depths of 75 to 90 m. It is bounded on the east and south by valleys and basins that reach depths of 115 to 185 m. The seabed in the northern part of this feature is relatively smooth with some low hills and is covered with gravel (patches of cobbles and boulders are present) that is partly covered with a veneer of sand. Long, narrow grooves in the seabed that typically are 50 to 100 m wide, less than 5 m deep, and up to 4 km long are interpreted to be marks made by the jagged bottoms of icebergs that gouged the seabed by grounding here during the late stages of the last glaciation. These grooves are shallower and less pronounced than similar features that occur in Quadrangles 15 and 18 (Valentine and others, 1999o, r), possibly because they have been partly filled by sand transported from the bank that lies to the northwest. The southern part of the feature exhibits low rounded hills and shallow, smooth-floored valleys and basins. The hills are covered with gravel, including boulder piles, and the gravel is covered in places by a thin veneer of sand that is most extensive on the hillsides. The floors of the shallow valleys and basins (42° 37.9'N, 70° 20.1'W; 42° 36.2'N, 70° 22.7'W) are covered with sand and muddy sand.

    A wide, deep glaciated valley extends from the northern edge of the quadrangle to its center where it divides into two valleys that extend southward around a large, elongated bank. The valley floors (125-185 m) are muddy sediment, except for some areas where sand has been transported into the valleys from neighboring banks. Hummocky, lobe-shaped depositional features extend into the valleys (42° 34.6'N, 70° 19.5'W) and southwestward from the base of the broad bank on the western edge of the quadrangle (42° 36.5'N, 70° 24.5'W). They are interpreted to have been formed by glacial debris (now covered by muddy sand) that was deposited by ice falls that flowed from the elevated surfaces of the banks and ridges.

    The large central bank bounded by these valleys has a relief of 60 to 100 m, and its surface is covered with sand and gravel, including boulder piles and ridges. Some of the boulder ridges resemble eskers (sand and gravel deposited by running water in channels within stationary glacial ice). Other ridges are located along the upper edges of glaciated valleys and are interpreted to be lateral moraines (deposits of rock debris piled up at the edges of moving ice).

    The eastern side of the quadrangle is characterized by low hills and shallow valleys, similar to features that occur in the adjacent Quadrangle 15 to the west. The low hills are covered with gravel, including boulder piles and ridges. The gravel is covered in places by a thin veneer of sand that is more extensive on the hillsides than on the hilltops. In the northeastern part of the quadrangle, the seabed displays iceberg scours similar to those described above from the western part of the quadrangle. In the southwestern part of the quadrangle, hills, complex ridges, and deep basins (140-150 m) display a range of sediment types. Generally, the hills are covered with gravel (including some boulder piles and ridges), the shallow valleys and depressions (42° 34.1'N, 70° 20.4'W) are sandy, and the deep valleys (42° 34'N, 70° 23'W) are muddy sand and mud.

Quadrangle 15 Features
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    The regional slope of the sea floor in Quadrangle 15 increases from approximately 70 m water depth in the southwest to 130 m in the east and northeast. The shallow and deep parts of the seabed are very different in character. The southwestern part of the quadrangle is characterized by low hills and shallow valleys (and one deep valley) that are related topographically to the well-defined banks and deep valleys that occur in the adjacent Quadrangle 14 to the west (Valentine and others, 1999n). The low hills are covered with gravel, including boulder piles and ridges. The gravel is covered in places by a thin veneer of sand that is more extensive on the hillsides than on the hilltops. Some of the linear boulder ridges (42° 33.9'N, 70° 11.4'W; 42° 35.2'N, 70° 09.2'W; 42° 35.4'N, 70° 12.0'W) resemble eskers (sand and gravel deposited by running water in channels within stationary glacial ice). Other ridges are located along the upper edges of shallow glaciated valleys (42° 33.9'N, 70° 11.9'W; 42° 35.65'N, 70°13.15'W) and are interpreted to be lateral moraines (linear deposits of rock debris formed at the edges of moving ice). The valleys are floored by sand. Lateral moraines also are present lower on the valley walls (42° 36.9'N, 70° 12.5'W and 42° 34.35'N, 70° 11.3'W). Broad depressions in the tops of some hills possibly indicate the former locations of large masses of melting ice (42° 34.8'N, 70° 09.0'W).

    The sea floor in the remainder of the quadrangle exhibits a southeast-trending grain of small hills and basins that probably reflect the movement of a regional ice sheet. The hills are low and rounded and typically have 5 to 10 m of relief. They are covered with gravel, (patches of boulders and cobbles are common) that is partly covered with a thin veneer of sand. Between the hills, the seabed is chiefly sand with patches of gravel with scattered cobbles and boulders. A series of elongate, shallow, southeast-trending basins is present in the central and southeastern part of the quadrangle. Some of the basins reach water depths of 120 to more than 150 m, and their floors are 15 to 20 m below the surrounding seabed. The floors of the deepest basins are relatively smooth and are covered with fine-grained sand and mud.

    The most striking topographic features in Quadrangle 15 are many long, narrow grooves that dominate all but the southwestern part of the map area. They typically are 50 to 100 m wide, up to 5 to 10 m deep, and up to several kilometers long. These grooves are interpreted to be marks made by the jagged bottoms of icebergs that gouged the seabed by grounding here during the late stages of the last glaciation. The iceberg grooves are most common in the deeper eastern part of the quadrangle, and they disappear in the 75 to 80 m depth interval in the shallow southwestern part of the quadrangle. The grooves appear to have a dominant northeast-southwest orientation. They become less distinct toward the southwest where they appear to be partly filled by sandy sediment transported from shallow areas in the western part of this quadrangle and the eastern part of Quadrangle 14.

Quadrangle 16 Features
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    The southern part of this quadrangle is a shallow bank that lies at water depths of 40 to 55 m. It is the westward extension of a large bank that lies mostly in the adjacent Quadrangle 17 to the east (Valentine and others, 1999q). The bank surface is gravel (including boulder piles and ridges) that is covered with a thin veneer of sand in low parts of the bank top. The boulder ridges are a complex of glacial features that resemble lateral and end moraines (deposits of rock debris piled up at the edges of glacial ice) and eskers (sand and gravel deposited by running water in channels within stationary ice). Several large depressions on the bank (42° 41.0'N, 70° 28.4'W and 42° 40.9'N, 70° 27.5'W) possibly mark the former locations of large masses of melting ice. The bank is incised on its northern edge by a north-trending valley (42° 42.5'N, 70° 29.5'W) that is floored by sand in its head and muddy sand where it enters a large basin. The southeastern corner of the quadrangle is part of the western flank of the large bank in Quadrangle 17. The seabed slopes northwestward through water depths of 40 to 75 m. It is gravel to a water depth of approximately 55 m; below this depth, the gravel is covered with a veneer of sand to 75 m.

    Low hills and elongate ridges extend northwestward from the eastern edge of the quadrangle into a large basin that occupies a major part of the region. The hills and ridges range through water depths of 70 to 100 m. They are covered with gravel, including boulder piles and ridges. The gravel is covered in places with a veneer of sand that is more extensive on the sides of these features than on their tops. A long, broad ridge extends northwestward across the upper part of the quadrangle and past the quadrangle=s northern boundary at 42° 48'N. The ridge has a relief of 15 m (80 to 95 m water depth) except for a high hill at 70° 33.5'W near the northern edge of the quadrangle. The ridge crest is covered with gravel, including boulder piles and ridges, and its flanks are covered with a thin veneer of sand.

    Long, narrow grooves in the seabed that typically are 50 to 100 m wide, less than 5 m deep, and up to a kilometer or more in length, are interpreted to be marks make by the jagged bottoms of icebergs that gouged the seabed by grounding here during the late stages of the last glaciation. They are present at 70 to 95 m water depth. Similar grooves are also present in the adjacent Quadrangle 17 to the east.

    Outcrops of bedrock are present in the far southwestern corner of the quadrangle. They lie at 15 to 55 m water depth and are an extension of rocks exposed on the coastline a mile to the west. The remainder of the sea floor in Quadrangle 16 is relatively smooth sandy mud and mud and is part of a basin that ranges in depth from 30 m in the southwest to 110 m in the northeast. Sediment in the basin becomes more muddy with increasing water depth in the transition areas surrounding bedrock outcrops, and gravelly banks, ridges, and hills.

    In several areas of the basin, the smooth mud seabed is interrupted by shallow depressions (42° 43.05'N, 70° 31.15'W; 42° 43.65'N, 70° 31.60'W; 42° 43.77'N, 70° 31.00'W). The depressions are irregular in outline and up to several hundreds of meters in length, and some of them surround small mounds. Observations of similar features in Quadrangles 7 and 8 (Valentine and others, 1999g, h) have shown them to be patches of gravel, including boulders, that are frequented by groundfish. The depressions in the mud are interpreted to have formed by the scouring actions of groundfish that have exposed the gravel habitat and prevent its burial by basin mud.

Quadrangle 17 Features
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    This quadrangle is bisected by a broad, northeastward-trending bank that lies at water depths of 35 to 65 m. The bank's surface is primarily gravel and includes numerous boulder piles and ridges. Boulder ridges oriented northeastward, parallel to the trend of the bank, are located mainly along the western side of the bank. They resemble end moraines (deposits of rock debris piled up at the forward edge of glacial ice). Boulder ridges that trend southeastward, across the bank, resemble eskers (sand and gravel deposited by running water in channels within stationary glacial ice). The bank=s western margin is a well-defined scarp (25 to 35 m of relief) that extends from water depths of 55 to 90 m in the north and from 50 to 75 m in the south. This margin is covered with sand and separates the bank from a basin of variable depth and seabed type.

    The basin is subdivided by a narrow ridge that extends northwestward from the bank. The ridge has a relief of 20 to 25 m and its surface lies at water depths of 75 to 80 m. It is covered with gravel (including boulder piles and ridges), and the gravel is covered in places with a thin veneer of sand. The ridge is bounded on the north and south by the deep parts of the basin (100-110 m) where the seabed is sandy mud. The basin shallows to the south along the western edge of the quadrangle where water depths range from 75 to 90 m. The basin floor here exhibits scattered small hills of gravel, in part with a veneer of sand, that are separated by a relatively smooth sea floor of muddy sand.

    The eastern edge of the bank south of approximately 42° 44'N is covered with sand intermixed with shell accumulations. The remainder of the eastern edge of the bank is mainly gravel except for a narrow band of sand that extends northward from a hill located at 42° 46.5'N, 70° 14.4'W. This hill has a relief of 25 m (30 to 55 m water depth). It is the easternmost and larger of a pair of distinctive conical hills that are outcrops of bedrock surrounded by sand and gravel of the bank surface. Approximately 2.7 km southeast of these two hills, a larger, conical hill is present along the eastern margin of the quadrangle (42° 45.3'N). This hill also is a bedrock outcrop. It has a relief of 100 m (35 to 135 m water depth) and lies mostly in the adjacent Quadrangle 18 to the west (Valentine and others, 1999r). The flanks and base of the hill are covered with coarse sandy and gravelly sediments.

    The southeastern part of the quadrangle is topographically complex. Two relatively deep basins are separated by a bank that slopes eastward from the central bank through water depths of 70 to 85 m. Along the bank's northwestern margin, there is an apron of coarse sand (at depths of 65 to 75 m) that was transported from the larger, shallower bank to the west. The bank surface exhibits low, rounded hills and small, shallow basins. The hills are covered with gravel, including boulder piles. The gravel is covered in places with a thin veneer of sand that is most extensive on the hillsides and in the shallow basins. Somewhat deeper basins and valleys on the southern margin of this bank are covered with muddy sand.

    Long, narrow grooves in the seabed that typically are 50 to 100 m wide and less than 5 m deep are interpreted to be marks made by the jagged bottoms of icebergs that gouged the seabed by grounding here during the late stages of the last glaciation. These grooves are shallower and less pronounced than similar features that occur in Quadrangles 15 and 18 (Valentine and others, 1999o, r), possibly because they have been partly filled by sand transported from the large bank that lies to the northwest.

    The two deep basins that are bounded to the west by the large central bank deepen eastward and are floored by muddy sand. The southern basin ranges in depth from 70 to 145 m, and the northern basin ranges from 70 to 135 m. A narrow, low ridge that parallels topography exends along the western margins of both basins, at the base of the central bank. These ridges are interpreted to be lateral moraines (deposits of rock debris piled up at the edge of moving ice) now covered by sand transported from the bank.

Quadrangle 18 Features
(click here to access individual quadrangle page in this browser window)

    In Quadrangle 18, the sea floor slopes regionally from approximately 85 m water depth in the southwest to 155 m in the northeast. Within this regional setting, the seabed is topographically variable and includes valleys, basins, hills, and a prominent hill that reaches a water depth of less than 35 m. The seabed in the southern and northeastern parts of the quadrangle exhibits a southeast-trending grain of small hills and basins that probably reflect the movement of a regional ice sheet. This is similar to the bottom type observed in the adjacent Quadrangle 15 to the south (Valentine and others, 1999o). These hills are low, rounded, typically have 5 to 10 m of relief, and are covered with gravel (including patches of boulders and cobbles) that is partly covered with a thin veneer of sand. Between the hills, the seabed is chiefly sand with patches of gravel and scattered cobbles and boulders.

    A series of elongate, shallow, east- and southeast-trending basins is present in the central and eastern parts of the quadrangle. The basins deepen from west to east. They reach water depths of 110 to 175 m and their floors are 10 to 35 m below the surrounding seabed. The basin floors are relatively smooth and are covered with fine-grained sand and mud; the percentage of mud increases from west to east with increasing water depth.

    The most striking topographic features in Quadrangle 18 are many long, narrow grooves that dominate all but the northwestern part of the map area. They typically are 50 to 100 m wide, up to 5 to 10 m deep, and some are 5 kilometers long. These grooves are interpreted to be marks made by the jagged bottoms of icebergs that gouged the seabed by grounding here during the late stages of the last glaciation. The iceberg gouges are first observed at 145 m water depth in the northeast corner of the quadrangle, and they disappear in the 70- to 75-m depth interval in the shallow northwestern part of the map area. The floors of many of the deeper basins (below 120 to 125 m) are too deep to have been marked by the grounded icebergs. The iceberg grooves have a dominant northeast-southwest orientation. They become less distinct toward the northwestern and southwestern corners of the quadrangle.

    A large, conical hill is located along the western margin of the quadrangle (42° 45.5'N) that has a relief of 100 m (35 to 135 m) on its southwestern flank. This feature is an outcrop of resistant bedrock whose shape has been modified by the scouring of glacial ice. The ice apparently moved from west to east, removing material from the eastern (or lee) side of the peak and forming eastward-trending grooves and ridges (1 to 2 km long) in the adjacent basin. The flanks and base of the hill are covered with coarse sandy and gravelly sediments.

    A similar, but smaller, bedrock hill is located approximately 3 km to the northeast (42° 45.9'N, 70° 10.9'W) of the large hill. It reaches a water depth of 50 m and has a relief of 75 m (50 to 125 m) on its southern flank. These features are similar in character to two small hills on Jeffreys Ledge in the adjacent Quadrangle 17 to the west (Valentine and others, 1999q). North of the large hill, a sinuous basin floored with sand is bounded on the east and west by gravelly seabed (patches of cobbles and boulders are common) that is partly covered by a thin veneer of sand.

References Cited

Massachusetts Bay Disposal Site Maps and Features on paper:
Valentine, P.C., Danforth, W.W., Roworth, E.T., and Stillman, S.T., 1996, Maps showing topography, backscatter, and interpretation of seafloor features in the Massachusetts Bay Disposal Site region off Boston, Massachusetts: U.S. Geological Survey Open-File Report 96-273, scale 1:10,000 and 1:12,500, 2 sheets.

Massachusetts Bay Disposal Site Maps and Features on CD-ROM:
Valentine, P.C., Baker, J.L., Unger, T.S., Evans, J., and Polloni, C., 1999, Sea floor topographic, backscatter, and interpretive maps and bottom photos of the Massachusetts Bay Disposal Site region off Boston, Massachusetts: U.S. Geological Survey Open-File Report 98-344, 1 CD-ROM.

Sea Floor Topography of Quadrangles 1-18 in Stellwagen Bank National Marine Sanctuary on paper:
Valentine, P.C., Baker, J.L., Unger, T.S., and Roworth, E.T., 1997a, Sea floor topography of Quadrangle 1 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-502, scale 1:25,000.

Valentine, P.C., Unger, T.S., Baker, J.L., and Roworth, E.T., 1997b, Sea floor topography of Quadrangle 2 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-503, scale 1:25,000.

Valentine, P.C., Baker, J.L., Unger, T.S., and Roworth, E.T., 1997c, Sea floor topography of Quadrangle 3 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-504, scale 1:25,000.

Valentine, P.C., Unger, T.S., Baker, J.L., and Roworth, E.T., 1997d, Sea floor topography of Quadrangle 4 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-505, scale 1:25,000.

Valentine, P.C., Baker, J.L., Unger, T.S., and Roworth, E.T., 1997e, Sea floor topography of Quadrangle 5 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-506, scale 1:25,000.

Valentine, P.C., Unger, T.S., Baker, J.L., and Roworth, E.T., 1997f, Sea floor topography of Quadrangle 6 in the Stellwagen Bank National MarineSanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-507, scale 1:25,000.

Valentine, P.C., Baker, J.L., Unger, T.S., and Roworth, E.T., 1997g, Sea floor topography of Quadrangle 7 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-508, scale 1:25,000.

Valentine, P.C., Unger, T.S., Baker, J.L., and Roworth, E.T., 1997h, Sea floor topography of Quadrangle 8 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-509, scale 1:25,000.

Valentine, P.C., Baker, J.L., Unger, T.S., and Roworth, E.T., 1997i, Sea floor topography of Quadrangle 9 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-682, scale 1:25,000.

Valentine, P.C., Unger, T.S., Baker, J.L., and Roworth, E.T., 1997j, Sea floor topography of Quadrangle 10 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-683, scale 1:25,000.

Valentine, P.C., Baker, J.L., Unger, T.S., and Roworth, E.T., 1997k, Sea floor topography of Quadrangle 11 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-684, scale 1:25,000.

Valentine, P.C., Unger, T.S., Baker, J.L., and Roworth, E.T., 1997l, Sea floor topography of Quadrangle 12 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-685, scale 1:25,000.

Valentine, P.C., Baker, J.L., Unger, T.S., and Roworth, E.T., 1997m, Sea floor topography of Quadrangle 13 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-726, scale 1:25,000.

Valentine, P.C., Unger, T.S., Baker, J.L., and Roworth, E.T., 1997n, Sea floor topography of Quadrangle 14 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-727, scale 1:25,000.

Valentine, P.C., Baker, J.L., Unger, T.S., and Roworth, E.T., 1997o, Sea floor topography of Quadrangle 15 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-728, scale 1:25,000.

Valentine, P.C., Unger, T.S., Baker, J.L., and Roworth, E.T., 1997p, Sea floor topography of Quadrangle 16 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-729, scale 1:25,000.

Valentine, P.C., Baker, J.L., Unger, T.S., and Roworth, E.T., 1997q, Sea floor topography of Quadrangle 17 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-730, scale 1:25,000.

Valentine, P.C., Unger, T.S., Baker, J.L., and Roworth, E.T., 1997r, Sea floor topography of Quadrangle 18 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 97-731, scale 1:25,000.

Sea Floor Topography of Quadrangles 1-18 in Stellwagen Bank National Marine Sanctuary on CD-ROM:
Valentine, P.C., Baker, J.L., and Unger, T.S., and Polloni, C., 1998, Sea floor topographic map and perspective view imagery of Quadrangles 1-18, Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Open-File Report 98-138, 1 CD-ROM.

Sun-Illuminated Sea Floor Topography of Quadrangles 1-18 in Stellwagen Bank National Marine Sanctuary on paper:
Valentine, P.C., Baker, J.L., and Unger, T.S., 1999a, Sun-illuminated sea floor topography of Quadrangle 1 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2701, scale 1:25,000.

Valentine, P.C., Unger, T.S., and Baker, J.L., 1999b, Sun-illuminated sea floor topography of Quadrangle 2 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2702, scale 1:25,000.

Valentine, P.C., Baker, J.L., and Unger, T.S., 1999c, Sun-illuminated sea floor topography of Quadrangle 3 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2703, scale 1:25,000.

Valentine, P.C., Unger, T.S., and Baker, J.L., 1999d, Sun-illuminated sea floor topography of Quadrangle 4 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2704, scale 1:25,000.

Valentine, P.C., Baker, J.L., and Unger, T.S., 1999e, Sun-illuminated sea floor topography of Quadrangle 5 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2705, scale 1:25,000.

Valentine, P.C., Unger, T.S., and Baker, J.L., 1999f, Sun-illuminated sea floor topography of Quadrangle 6 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2706, scale 1:25,000.

Valentine, P.C., Baker, J.L., and Unger, T.S., 1999g, Sun-illuminated sea floor topography of Quadrangle 7 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2707, scale 1:25,000.

Valentine, P.C., Unger, T.S., and Baker, J.L., 1999h, Sun-illuminated sea floor topography of Quadrangle 8 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2708, scale 1:25,000.

Valentine, P.C., Baker, J.L., and Unger, T.S., 1999i, Sun-illuminated sea floor topography of Quadrangle 9 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2709, scale 1:25,000.

Valentine, P.C., Unger, T.S., and Baker, J.L., 1999j, Sun-illuminated sea floor topography of Quadrangle 10 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2710, scale 1:25,000.

Valentine, P.C., Baker, J.L., and Unger, T.S., 1999k, Sun-illuminated sea floor topography of Quadrangle 11 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2711, scale 1:25,000.

Valentine, P.C., Unger, T.S., and Baker, J.L., 1999l, Sun-illuminated sea floor topography of Quadrangle 12 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2712, scale 1:25,000.

Valentine, P.C., Baker, J.L., and Unger, T.S., 1999m, Sun-illuminated sea floor topography of Quadrangle 13 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2713, scale 1:25,000.

Valentine, P.C., Unger, T.S., and Baker, J.L., 1999n, Sun-illuminated sea floor topography of Quadrangle 14 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2714, scale 1:25,000.

Valentine, P.C., Baker, J.L., and Unger, T.S., 1999o, Sun-illuminated sea floor topography of Quadrangle 15 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2715, scale 1:25,000.

Valentine, P.C., Unger, T.S., and Baker, J.L., 1999p, Sun-illuminated sea floor topography of Quadrangle 16 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2716, scale 1:25,000.

Valentine, P.C., Baker, J.L., and Unger, T.S., 1999q, Sun-illuminated sea floor topography of Quadrangle 17 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2717, scale 1:25,000.

Valentine, P.C., Unger, T.S., and Baker, J.L., 1999r, Sun-illuminated sea floor topography of Quadrangle 18 in the Stellwagen Bank National Marine Sanctuary off Boston, Massachusetts: U.S. Geological Survey Geologic Investigations Series Map I-2718, scale 1:25,000.