A petroglyph is a carving in a rock, usually a prehistoric carving in a rock. A petroglyph may be picked, pecked, incised or abraded. The word petroglyph enters the English language in 1870, taken from the French word pétroglyphe, which is in turn derived from the Greek petro-, meaning rock, and gluphē, meaning carving.
A pictograph is a picture that is used as a symbol for an idea or word, it is painted on top of the rock, not carved into the rock. Pictographs are usually prehistoric, they are the earliest type of written human communication. The word pictograph was first used in 1851 in reference to American Indian rock art, derived from the Latin word pictus which means painted, and the suffix -graph which means something written.
Examples
Fittingly, the front of the building will feature a petroglyph that depicts a drawing of the mound and surrounding area as it appeared in the early 19th century. (The Times Daily)
Because these petroglyphs have been undisturbed, they have built up into what is reputedly the world’s most extensive and diverse assemblage of rock engravings, set against the North-West Shelf gas project, which is the biggest resource project ever undertaken in Australia. (The Western Australian)
Positioned on cliffs seventy feet high on the private land of Kay Campbell, there are hundreds of pictographs portraying both human and animal figures, as well as curious geometric shapes, and both negative (outlined) and positive handprints. (The San Antonio Examiner)
Others include pictographs, or paintings on rocks; birch bark scrolls handed down through generations; and effigy earth mounds, huge mounds in stylized animal or symbol shapes used for burial or storage caches and once common throughout Michigan and the Midwest. (The Detroit Free Press)