n. A carving or drawing on rock, especially one made by prehistoric humans; called also a petrograph. [ PJC ]

{ } a. Pertaining to petrography. [ 1913 Webster ]

n. [ Petro + -graphy. ] 1. The art of writing on stone. [ 1913 Webster ]

2. The scientific description of rocks; that department of science which investigates the constitution of rocks; petrology. [ 1913 Webster ]