"i believe my ancestors were gypsies so i do not know if this has any relevance"That's interesting. Where Battersea Park is today used to be marshland, and it could be that your ancestors were living there gypsy-style, and the only address that could be given was "marsh".I wonder if the baby was included in the 1851 census, which is available at the National Archives at Kew, or online at http://www.nationalarchives.gov.uk/census
Richard Jennings ● 6937d