Appears this male Clark (father of Sarah Rebecca Clark) is either Joseph Clark (born ca. 1785) or the son of Joseph Clark of Martic Township, born 1801. He and his wife, Rebecca, and children could be living with his parents in 1840. This Joseph is a neighbor of George and Joshua Hagen and is no longer listed in the 1850 census where Rebecca and children are still located next to the Hagens.
Joseph married Rebecca Flemming. (Rebecca Flemming was born on 16 Apr 1808 in Pennsylvania, died on 6 Feb 1883 in Martic Township, Lancaster PA. and was buried in Mt. Nebo Presbyterian Cemetery, Lancaster Co., PA ... aka Clarks Family Burying Ground.)