Are there any online maps that show....

Are there any online maps of the coast that show bottom type ie: rocky or sandy?

http://walrus.wr.usgs.gov/morphology/prelim.html

Most charts just give depth contours, some say "rocky" in areas to indicate a reef.  Other times you can just tell.  They usually mark kelp and offshore rocks, which are an indication of a reef system in the area as well.