Funding for this research was provided by the Coastal and Marine Geology Program of the U.S. Geological Survey and the Massachusetts Office of Coastal Zone Management.  We wish to thank Anthony Wilbur, Bruce Carlisle, and Daniel Sampson for their encouragement and support of offshore research.  Assistance in the field was provided by Bill Danforth, Dave Foster, Barry Irwin, Tom O'Brien, Dann Blackwood, Chuck Worley, Emile Bergeron, Emily Himmelstoss, Elizabeth Pendleton, Sandy Baldwin, and Brian Buczkowski and the captains and crews of the RV Megan T. Miller and RV Connecticut.  Jennifer Martin arranged this document in HTML.  This manuscript benefited from reviews by Emily Himmelstoss, Elizabeth Pendleton and VeeAnn Cross. We also thank the staff of NOAA's National Geophysical Data Center for providing data from NOAA hydrographic survey H10993.