a market-town of Buckinghamshire, about twenty-seven miles westward of London. It is situated in 4° W. long. and 51° 40' N. lat. and sends two members to parliament.

AMETHYSTUS, amethyst, a transparent gem of a purple colour, arising from a mixture of red and blue. However, their colour is various: Some have a mixture of yellow, and some resemble red wine and water; but the best kind is transparent and colourless, and resembling so much the diamond, that the difference can only be distinguished by the softness of the amethyst. This gem is found of various sizes, from the bulk of a small vetch, to an inch and an half in diameter. Its shape is sometimes roundish, sometimes oblong, and sometimes flattened a little on one side; but its most common figure is that of a crystal, composed of four planes, and terminated by a flat short pyramid. The amethyst is found in India, Arabia, Armenia, Ethiopia, Cyprus, Germany, Bohemia, and Mithra; but as they are generally as soft as crystal, they are not much valued. It may be counterfeited many ways; but the Germans hardly think it worth the counterfeiting.