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 ]