Don't know if it any help but I have found this:
1841 has an Alexander Marrack age 40 Clarence Street, Madron, Penzance Union, Cornwall, England Archive reference HO107 Piece number 143 Book number 3 Folio number 55 Page number 25.
and Alexr Marrack age 58 at Regent Terrace, Madron, Penzance Union, Cornwall, England.Archive reference HO107 Piece number 143 Book number 2 Folio number 52 Page number 19.