There are real cool petroglyphs out there. Seem like many like leaving marks on or carving rocks to some extent. From Mount Rushmore to the graffiti artist, they follow the primitive urge to leave their mark. It's the human mark.

Petroglyphs are found world-wide and are most often associated with prehistoric people. Greek words petros meaning "stone" and glyphein meaning "to carve" (it was originally coined in French as pétroglyphe).

The term petroglyph should not be confused with the term pictograph, which is similar to a graffiti image drawn or painted on a rock face. Early forms date back to 9000 BC.

A pictogram is a pictograph representing a concept, activity, object or place by rendering an illustration. These forms of expressions have transformed into pictograms serving as signs or instruction everywhere. They are easy to understand because of graphical realistic depictions of the action being advertised.

Petroglyphs and pictographs image belong to the wider and more general category of rock art. Rock art includes anything drawn, carved, engraved, inscribed, painted or sculpted into rock.

* Petroglyphs - carvings into stone surfaces

* Pictographs - rock and cave paintings

* Petroforms and the Inukshuks of the Canadian Arctic are rock art made by aligning or piling together natural stones.