Arrastra

An Arrastra (or Arastra) is a primitive mill for grinding and pulverizing (typically) gold or silver ore. The simplest form of the arrastra is two or more flat-bottomed drag stones placed in a circular pit paved with flat stones, and connected to a center post by a long arm. With a horse, mule or human providing power at the other end of the arm, ...
Found on http://en.wikipedia.org/wiki/Arrastra

arrastra

crude drag-stone mill for pulverizing ores such as those containing silver or gold or their compounds. See patio process.[1 related articles]
Found on http://www.britannica.com/eb/a-z/a/104

ARRASTRA

A mill, consisting of one or more large stones dragged around on a circular bed, used to grind ore.
Found on http://www.nchistoricsites.org/reed/glossary.htm
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