Marriage records in the Historical Records on FamilySearch.org
Bryan Lowther has Frederick's name as Frederick Sylvester Harrison. Listed as Frederick M. in the 1910 Census. As this is Mr. Lowther's ancester, I would think Sylvester to be correct.
1920 Census. Van Buren Twp, Crawford Co, AR Hh 174
Frederick S. HARRISON and Cardelia VANDERGRIFF were married on 28 June 1913 in Sebastian County, Arkansas.62 Cardelia VANDERGRIFF, daughter of Andrew Jackson VANDERGRIFF and Mary Jane GREGORY, was born on 15 April 1894 in Arkansas.62 She died on 8 February 1988 at the age of 93.62
Frederick S. HARRISON and Cardelia VANDERGRIFF had the following children: