There are several songs that occasionally have the title "Mary Mack." The most common one is a children's song, "Mary Mack, Mack, Mack, Dressed in black, black, black...." It is very often used as a clapping game. The earliest version I know is from Halliwell's The Book of Nursery Rhymes Complete, in 1846. It's available on Google Books; look for "Parson Darby wore a black gown" and "Darby and Joan were dress'd in black."

It's clearly traditional, but based on the distribution of nineteenth century versions, I would suspect it is English, not Scottish.

There is also a fairly well-known music hall song with this title. That is the one listed in the Digital Tradition under the title "Mary Mack."