30	NATURAL HISTORY OF GEMS.
	the hardest of all geins, and only to be touched by the Diamond-point. Intagli of all dates and in every style occur upon Amethysts, but so much more generally on the pale sort that an engraving upon one of a rich dark colour may, on that very ground, be suspected as modern. Besides the foregoing remarks as to the high value of such a shade in antiquity, the modern artists have usually employed the Hungarian Amethyst as being now the most abundant, of which the tint is a fine reddish purple, though the lustre is far below that of the Indian. Amongst the few exceptions to this rule that have come under my own notice is a head styled of Mithridates, but, in my judgment of some Bactrian king of the line of Euthydemus ; perhaps the noblest Greek portrait in existence, cut in a large Amethyst of the deepest violet colour, found a century ago in India ; which, however, being doubtless the royal signet, rather corroborates than weakens the previous statement. For such a use the most precious material procurable would naturally have been selected; "ut alibi ars, alibi materia esset in pretio," to use Pliny's expression. Another fine Greek intaglio, a head of Pan, in front face, on a similar stone, the antiquity of which could not be called in question, was in the Uzielli Cabinet; and, above all, stands the unrivalled Marlborough Omphale, the first amongst the numerous repetitions of that favourite subject, where the Amethyst (of the Indian kind) possesses equal lustre and richness of colour. In a large circular, convex stone of this sort is engraved the Berlin Atalanta, justly styled by Winckelmann "une des gravures les plus parfaites qu'on puisse voir." The swift -foot nymph is figured running at full speed and holding down with both hands the folds of her voluminous pepium distended by the agitated air. Through its gauzy material