Clock is possibly a variation of Glock, a Germanic surname indicating one's ancestors lived by the bell tower of a church. Hanks & Hodges's
A Dictionary of Surnames gives Clocke as the Flemish form and Klok and Klokke as Dutch forms of Glock.
My Dutch name dictionary (
Woordenboek van Voornamen by J.
Van Der Schaar) says that Marchien is used as a pet form of both
Margareta and
Maria in the province of Drenthe in the Netherlands.