MLA

Puzzle-cause, Oliver. A Curious Letter from Oliver Puzzle-Cause. s.n., 0AD. https://collections.library.yale.edu/catalog/17124818.

APA, 6th edition

Puzzle-cause, O. (0 C.E.). A curious letter from Oliver Puzzle-cause [Early works to 1800, Broadsides, Letters]. s.n. https://collections.library.yale.edu/catalog/17124818.