Well, that's an interesting thought.It would be nice if the name Terrell gave us a clue to his mother's identity.
I have noticed from deeds, etc., that there was a Terrell family living near George Cockburn in Franklin Co., Georgia. For example, an abstract of the Deeds of Franklin County, Georgia 1784-1826,” states:
Deed Book OO, Page 17: DEED dated 26 June 1797, rec. 25 April 1803, from HEZEKIAH TERRELL of Franklin Co. to SAMUEL WHITAIRE of aforesaid. In cons. of $13, conveys Lot #8 in Carnesville, adj. Redfern Wims and George Cockburn, being whereon said Whitaire now lives “nearly opposite to Harris Wyly.” Wit: Harris K. Wyly, James Terrell, J.P.
I believe that Clark might have been named for this family.Perhaps they were relatives as well ...