Definition of "sartin"

If the marrow in one's backbone should melt, it would be sartin to run out at the tip of one's tail.

1841, Various, Punch, Or The London Charivari, Vol. 1, July 17, 1841‎

This here's a mountain fireplace, sartin sure.

1910, Edward Marshall, Charles T. Dazey, In Old Kentucky‎