I have the information you are seeking on Seneca Marcy. I am descended from his sister Jemima, who was asked to write the names and DOB for her siblings,The letter is dated 2 Jan 1859. Seneca was born 11 Mar 1814. His siblings were Maria-21 Jul 1816, James-17 Mar 1818, Job-28 Jan 1821, Mary-9 Mar 1823, Amanda-1 May 1825, Jemima-21 Mar 1827, John-16 Jun 1830, Margaret-1 Dec 1832, George-6 Apr 1835, and William H.-12 Oct 1837. Parents were Benjamin Marcy and Salina Spencer. I have more generations. Let me know I'm glad to share. Will be happy to send photocopies of what I have.