Concise Oxford Dictionary of Archaeology (485 page)

 
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Photographic image taken from an aircraft or similar high-level elevated platform where the camera direction is at an angle to the ground beneath. Such photographs do not need special equipment, and using carefully chosen views and good lighting can provide a good impression of a complicated set of remains. However, oblique aerial photographs distort perspective and cannot easily be used for plotting and mapping visible features without rectification. See also
VERTICAL AERIAL PHOTOGRAPH
.

 
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Type of early Mesolithic
MICROLITH
found very extensively in northern Europe and elsewhere, essentially a narrow flint blade that has been backed or blunted along one edge towards the tip.

 
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A naturally occurring black volcanic glass extensively used in the production of edged tools. It fractures at the molecular level and produces some of the sharpest edges known on stone tools. One of the largest exploitation sites is on the Cycladic island of Melos but other sources are known at Lipari, Sicily, on Sardinia, in central and eastern Turkey, and in Hungary. Obsidian was exported widely around the eastern Mediterranean. In the Americas obsidian is found in Mexico. It also occurs in southeast Asia and in the Pacific, including important sources in Melanesia; obsidian from Talasea was traded from at least 17000 bc. There are also many sources in New Zealand.

 
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A method that is able to determine the age of an obsidian tool in terms of when it was made. When obsidian is chipped a thin layer of hydrated rock slowly builds up on the fresh surface. The thickness of the hydration layer can be measured as the basis for an estimate of how long ago the surface was exposed. The technique can be used back to about 25000 years ago, but there are always difficulties using the technique because the rate of hydration varies in relation to the chemical composition of the obsidian and the local environment in which it is preserved.

 
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Tuberous plant (Oxalis tuberosus) native to Andean South America. Domesticated as a root crop by
c.
ad 1500.

 
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