Ancestry would have you believe it's Sholtone. If I'm not mistaken he says he was born in Irvine in 1851....and there is an OPR birth in Dundonald in 1819 that surely looks possible.
A neighbor search on the 1881 census disks pops up one person stating they were born Sholton, Dundonald, Ayrshire.
Janet MILTON M 46 F Sholton Dundonald, Ayr, Scotland
Hey it works for me!
Best wishes
Jean