Bruce: Your grandfather must be Jonathan A. Burton. Okay, here's how it goes, although the spelling is different (McGruder/Magruder, all the same): 1. Alexander Magruder, the Immigrant 2. Samuel Magruder married Sarah Beall 3. Samuel Magruder married Eleanor Wade 4. William Mills Magruder married Joanna ? 5. Zephaniah Magruder married Frances Sublett 6. Zachariah Magruder, b. 1815, VA +(1st wife) Sarah Ann E. Burton, married 2/3/1845, VA; b. 1818, VA; d. 8/13/1855 (d/o Benjamin Burton and Elizabeth Jennings) Zachariah and Sarah had Adelaide, born 1845, died 1864; Rosabelle born 1848, VA, died 1871, VA married Jonathan A. Burton; L. Susan, born 1849, VA married William J. Carmack; Leander born 1851; and Laura Ann Magruder, born 1850, died 1855.
Try the Magruder forum. All of this information is in a book published by myself and Don McGruther. The book also has a CD on American Magruders that is over 1,700 pages long.