224                 NATURAL HISTORY OF GEMS.
	Selene. The greater porportion, however, was clue to hie own collecting, which he had prosecuted with unremitting zeal. Veltheim ('Onyx-gebirge,' p. 75) correctly supposes that such vases were cut in nodules (Nieren), made up of con­centric layers of Jasper and Calcedony, like the well-known Agate nodules. The ancient artist, adapting the form oi his vase with admirable skill to the natural disposition oi the strata in the stone under his hands, obtained a white coating enveloping the coloured body of the vase, through which ho cut down to the dark field, thus producing designs in cameo. As works of art, these vases possess considerable merit ; but infinitely more extraordinary arc they, regarded as mineralogical specimens, as will appear upon the con­sideration of the dimensions of tho principal examples pre­served. Of these, the most famous is the " Cup of the Ptolemies," a carchesium, or two-handled vase, holding a sextarius (above a pint), being 4-4/5 inches high, by 15| in circumference, measured over the handles. It is covered with masks, vases set out upon a table under a vine from whose branches depend oscilla, and other Bacchic emblems, admirably executed in relief ; and hence its popular appellation, from the assumption based upon these embel­lishments, that it could have been executed for no other than Ptolemy XI., surnamed Dionysos. The style, how­ever, is much more that of the times of Nero, a great dilettante, as Pliny records, in murrhine and crystal vases ; in fact, on one of his coins (in small brass), the reverse presents a table supporting similar articles, and altogether recalling the ornamentation of this carchesium. By a sin­gular coincidence, we find here a Dionysiac utensil dedi­cated to the service of a St. Dionysius, and reverting to its original destination. For after its presentation in the ninth century, by Charles III. (the Simple) to the abbey of