NameKezziah Mercer 
Spouses
Birthabout 1815
Memo(age 35 in 1850)
Deathbefore 17 January 1908
Memo(obituary date)
Marriage12 February 1840, Clark, VA
Marr Memo(VA Compiled Marriages, 1740-1850, on Ancestry.com)
Birth, Parent-Proof, Designation notes for William (Spouse 1)
I don’t know who this man is for sure but I found his marriage record in 1840 to Kezziah Mercer in Clarke County, VA. I note three things — his name is consistently spelled Marts, his wife’s name is Mercer (an English sounding moreso than German sounding name) and the only other Mærtz I know of Clarke County is John C who ives there in 1850.
Everything suggests that William is related to the Jacob Chamberlain Marts family and I believe he was likely the son of John C Martas. William is designated U3a1.