Prehistoric inscriptions

large geoglyphs made in the soil of the Nazca Desert in Peru

thumb|upright=1.35|Sampling of US National Park Service pictograms

thumb|upright|Geoglyphs on deforestation|deforested land in the Amazon rainforest A geoglyph is a large design or motif – generally longer than – produced on the ground by durable elements of the landscape, such as stones, stone fragments, gravel, or earth. A positive geoglyph is formed by the arrangement and alignment of materials on the ground in a manner akin to petroforms, while a negative geoglyph is formed by removing part of the natural ground surface to create differently coloured or textured ground in a manner akin to petroglyphs.

set of geoglyphs in the Brazilian state of Acre

thumb|A footprint (replica shown) carved into the rock on Dunadd, in [[Argyll, is linked to the crowning of the Scots kings of Dál Riata.]]

Stone with mysterious markings