The image below is of two netsinkers I recently found exposed on a river shoreline in Erie County, New York.  Netsinkers are simply flat pebbles that have been crudely notched to facilitate attachment to a fishing net.  The specimen on the right (8.5 cm x 8 cm) is of classic form for this artifact type.  Netsinkers are common on both Archaic and Woodland riverine occupation sites.