194                 NATURAL HISTORY OF GEMS.
	expression of filing a gem, the designs having evidently been cut into the circumference by rubbing with the edge of a fragment of Emery. It is at a more advanced period of Assyrian art that we perceive the neatly turned and regular indentations marking the application of the drill. The backs also of most really antique intagli of all periods show by the deep furrows upon them, but imperfectly con­cealed by the lustrous polish subsequently imparted, how the gems had literally been filed into shape by the rubbing with an Emery-stone. Hence we discover why Armenia should be famous for the production of the best material for this purpose ; it was the source from which tho inventors of the art drew their supplies of the indispensable agent. As the know­ledge of gem-engraving spread from Assyria towards the coast of Asia Minor, the artists carried with them a supply of the Armenian mineral. Theophrastus shows that in his days it was still imported from that region into Greece, although tho isle of Naxos then as now possessed inexhaustible mines. From the preference given by the Greeks, at the time when the Glyptic art had reached id highest point amongst them, to the Armenian kind, there is reason to suspect that the latter was a purer Corundum than the Naxian, and therefore more efficient in engraving. Modern times supply an analogous case in the same pro­cess. The Adamantine Spar, when introduced shortly be­fore 1790 (Easpe) into the European lapidary's atelier from India, where it had been known from time imme­morial, was eagerly received and immediately adopted universally as an enormous improvement upon the old-fashioned Emery-powder. It is self-evident that the Greeks would not have taken the trouble to import from a long distance, Armenia, precisely the same mineral as they were at the very time obtaining from their immediate neighbour-