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Petroglyphs are images created by removing part of a rock surfaces by incising, pecking, carving, and abrading. Outside North America, scholars often use terms such as "carving", "engraving", or other descriptions of technique to refer to such images. Petroglyphs are found world-wide, and are often (but not always) associated with prehistoric peoples. The word comes from the 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 pictograph, which is an image drawn or painted on a rock face. Both types of image belong to the wider and more general category of rock art. Petroforms, or patterns and shapes made by many large rocks and boulders in rows over the ground, are also quite different.
The oldest petroglyphs are dated to approximately the Neolithic and late Upper Paleolithic boundary, about 10,000 to 12,000 years ago. Around 7,000 to 9,000 years ago, other precursors of writing systems, such as pictographs and ideograms, began to appear. Petroglyphs were still common though, and some less advanced societies continued using them much longer, even until contact with Western culture was made in the 20th century. Petroglyphs have been found in all parts of the globe except Antarctica with highest concentrations in parts of Africa, Scandinavia, Siberia, southwestern North America and Australia.
There are many theories to explain their purpose, depending on their location, age, and the type of image. Petroglyphs are often thought to be astronomical markers, maps, and other forms of symbolic communication, including a form of "pre-writing". They might also have been a by-product of other rituals: sites in India, for example, have been identified as musical instruments or "rock gongs". <ref>Ancient Indians made 'rock music', BBC News Friday, 19 March, 2004</ref>
Petroglyph images probably had deep cultural and religious significance for the societies that created them; in many cases this significance remains for their descendants. Many petroglyphs are thought to represent some kind of not-yet-fully understood symbolic or ritual language. Later glyphs from the Nordic Bronze Age in Scandinavia seem to refer to some form of territorial boundary between tribes, in addition to possible religious meanings. It also appears that local or regional dialects from similar or neighboring peoples exist. The Siberian inscriptions almost look like some early form of runes, although there is not thought to be any relationship between them. They are not yet well understood.
Some researchers have noticed the resemblance of different styles of petroglyphs across different continents; while it is expected that all people would be inspired by their surroundings, it is harder to explain the common styles. This could be mere coincidence, an indication that certain groups of people migrated widely from some initial common area, or indication of a common origin. In 1853 George Tate read a paper to the Berwick Naturalists' Club at which a Mr John Collingwood Bruce agreed that the carvings had "... a common origin, and indicate a symbolic meaning, representing some popular thought." <ref>History of Rock Art study</ref> In his cataloguing of Scottish rock art, Ronald Morris summarised 104 different theories on their interpretation. <ref>Ronald Morris, The Prehistoric Rock Art of Galloway and The Isle of Man (ISBN 0-7173-0975-8 , Blandford Press 1979</ref>.
Other, more controversial, explanations are mostly grounded in Jungian psychology and the views of Mircea Eliade. According to these theories it is possible that the similarity of petroglyphs (and other atavistic or archetypal symbols) from different cultures and continents is a result of the genetically inherited structure of the human brain.
Other theories suggest that petroglyphs were made by shamans in an altered state of consciousness, perhaps induced by the use of natural hallucinogens. Many of the geometric patterns (known as form constants) which recur in petroglyphs and cave paintings have been shown to be "hard-wired" into the human brain; they frequently occur in visual disturbances and hallucinations brought on by drugs, migraine and other stimuli.
Present-day links between shamanism and rock-art amongst the San people of the Kalahari desert have been studied by the Rock Art Research Institute (RARI) of the University of the Witwatersrand . Though the San people's artworks are predominantly paintings, the beliefs behind them can perhaps be used as a basis for understanding other types of rock art, including petroglyphs. To quote from the RARI website:
- Using knowledge of San beliefs, researchers have shown that the art played a fundamental part in the religious lives of its San painters. The art captured things from the San’s world behind the rock-face: the other world inhabited by spirit creatures, to which dancers could travel in animal form, and where people of ecstasy could draw power and bring it back for healing, rain-making and capturing the game.
 The West Virginia controversy
The West Virginia glyphs are worth noting for the controversy that erupted over them in the 1980s. Barry Fell, a retired professor of marine biology at Harvard University, published an article in 1983, describing how he had deciphered petroglyphs in several places in southern West Virginia to have been written in Ogam, an Irish Celtic script dating back to the 6th to 8th century AD, and that they were in fact a detailed description of the nativity of Christ.  Fell is noted as promoting a theory of North America as having been visited by Irish, Iberian, Libyan, and Egyptian explorers "some 2,000 to 2,500 years ago".
In fact, Fell's methods involved an almost arbitrary grouping of markings, an interpretation of them as the only consonants of Ogam, and the addition of vowels and horizontal stem lines where he saw fit. This allowed him to decide which of three consonants each glyph should represent. Fell's work was subsequently debunked by linguists and archaeologists from several countries , to which Fell responded by accusing them of being "too damn lazy" to read his writings, and of being "ignorant".
Even those who agreed with Fell's interpretation of the marks as being Ogam disagree with his translation. Edo Nyland believed the "inscription" at Horse Creek to be in Basque and translated it very differently, as a description of a bison hunt. For instance, the section which Fell translates as "A happy season is Christmas, a time of joy and goodwill to all people." is given by Nyland (1996) as "Club blows in abundant measure (were needed) because many which had fallen into the ravine resisted with obviously broken legs. Brothers, come and help the slaughterer to finish them off."  Any interpretation which leads to such radically different interpretations should be treated with caution. Unfortunately, Fell's dubious Ogam theory has influenced many subsequent interpretations of carvings and paintings all over America.
 List of petroglyph sites
- Tassili n'Ajjer in Algeria
- Bidzar, Cameroon
- Bambari, Lengo and Bangassou in the south of the Central African Republic; Bwale in the west
- Niola Doa, Chad
- The Niari River valley in the Congo, 250km south west of Brazzaville
- Ogooue River Valley, Gabon
- Akakus, Libya
- Jebel Uweinat, Libya
- The Draa River valley in Morocco
- Twyfelfontein, Namibia
- Life-size giraffe carvings on Dabous Rock, Air Mountains, Niger
- Bangudae Petroglyphs, Korea
- Bhimbetka, India
- Rock art and petroglyphs in Northern Areas, Pakistan
- Burrup Penninsula, Dampier, Western Australia - Nominated World heritage Listing
- Arnhem Land / Kakadu National Park, Northern Australia
- Eight sites in Hong Kong: on Tung Lung Island, Kau Sai Chau, Po Toi Island, Cheung Chau, Shek Pik on Lantau Island, Wong Chuk Hang and Big Wave Bay on Hong Kong Island, Lung Ha Wan in Sai Kung
- Chumysh River basin, Kazakhstan, close to Bishkek (capital of neighbouring Kyrgyzstan)
- Several sites in Kyrgyzstan, mostly in the Tien Shan mountains; Cholpon-Ata, the Talas valley, Siymaliytash (Saimaluu-Tash), and on the rock outcrop called Suleiman's Throne in Osh in the Fergana valley
- Angono Petroglyphs of Rizal, Philippines
- Rongorongo of the Rapa Nui
- Hawaii (particularly the Big Island).
- Edakkal Caves, Wayanad District, Kerala, India
 South America
 North America
- Arches National Park, Utah
- Capitol Reef National Park, Utah
- Death Valley National Park, California
- Dinosaur National Monument, Colorado and Utah
- Horsethief Lake State Park, Washington
- Jeffers Petroglyphs, Minnesota
- Kanopolis State Park, Kansas
- Kejimkujik National Park, Nova Scotia
- Lava Beds National Monument, Tule Lake, California
- Newspaper Rock State Historic Monument, Utah
- Olympic National Park, Washington
- Petit Jean State Park, Arkansas
- Petrified Forest National Park
- Petroglyph National Monument
- Petroglyphs Provincial Park, north of Peterborough, Ontario
- Petroglyph Provincial Park, Nanaimo, British Columbia, Canada 
- Sloan Canyon National Conservation Area, Nevada
- South Mountain Park, Arizona
- Three Rivers Petroglyphs, New Mexico 
- West Virginia glyphs
- Writing Rock State Historical Site, North Dakota
- Writing-on-Stone Provincial Park, East of Milk River, Alberta
- Sedona, Arizona
- White Tank Mountain Regional Park, Waddell, Arizona
- St John, USVI
- Cup and ring marked rocks in Northumberland, County Durham and North Yorkshire, England
- Rock carvings in Tanumshede. World Heritage's site, Sweden
- Rock carvings at Alta, Norway
- Rock carvings at Møllerstufossen, Norway
- Rock carvings in Central Norway
- Mercantour National Park, France
- Newgrange, Ireland
- Bagnolo stele, Italy
- Stone stelae of the Ukraine
- Vale do Côa rock carvings, Portugal
 Middle East
- Wadi Rum, Jordan
- Wadi Faynan, Jordan
- "Graffiti Rocks", about 110 km SW of Riyadh off the Mecca highway
 See also
- Cave painting
- Rock art
- Cup and ring mark
- History of communication
- Megalithic art
- Parietal art
- Rune stone
 Further reading
- Beckensall, Stan and Laurie, Tim, Prehistoric Rock Art of County Durham, Swaledale and Wensleydale, County Durham Books, 1998 ISBN 1-897585-45-4
- Beckensall, Stan, Prehistoric Rock Art in Northumberland, Tempus Publishing, 2001 ISBN 0-7524-1945-5
 External links
- Dampier petroglyphs
- Reports of concerns for Australia's heritage
- The Rock Art Pages
- Petroglyph Provincial Park Official Website
- Northumberland Rock Art
- Debunking of Ogam theory about West Virginia petroglyphs
- A rival interpretation of the West Virginia petroglyphs
- Kyrgyz petroglyphs
- Cholpon-Ata petroglyphs, Kyrgyzstan
- Giraffe carvings on Dabous Rock, Air Mountains, Niger
- Rock engraving sites in Central Africa
- Shamanism and rock art among the San people of the Kalahari
- Rock Art Research Institute website (Witwatersrand)
- Rock Art Studies: A Bibliographic Database Bancroft Library's 14000+ citations to rock art literature.da:Helleristning
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