No one however will suppose that this earth was the same as that to which we at present give the name of _creta_, chalk; for if it was a natural earth it must have been of that kind called potters’ clay, as that clay is capable of receiving an impression and of retaining it after it is hardened by drying. That the Romans, under the indefinite name of _creta_, often understood a kind of potters’ earth, can be proved by many passages of their writers. Columella speaks of a kind of chalk of which wine-jars and dishes were made[352]. Virgil calls it tough[353]; and the ancient writers on agriculture give the same name to marl which was employed to manure land[354]. Notwithstanding all these authorities, I do not clearly comprehend how letters could be sealed with potters’ clay, as it does not adhere with sufficient force either to linen, of which in ancient times the covers of letters were made, or to parchment; as it must be laid on very thick to have a distinct impression; as it is long in drying, and is again easily softened by moisture; and, at any rate, if conveyed by post at present, it would be crumbled into dust in going only from Hamburg to Altona. I can readily believe that the Roman messengers employed more skill and attention to preserve the letters committed to their care than are employed by our postmen; but the distance from Asia to Rome is much greater than that from Hamburg to Altona. But may there not be as little foundation for the ancient expression _creta Asiatica_, Asiatic earth, as for the modern expression, _cera Hispanica_, Spanish wax? May not the former have signified a kind of coarse artificial cement? These questions might be answered by those who have had an opportunity of examining or only seeing the _sigilla cretacea_ in collections of antiquities. We are assured that such are still preserved; at least we find in Ficoroni[355] the representation of six impressions which, as he tells us, consisted of that earth. In that author however I find nothing to clear up my doubts; he says only that some of these seals were white; others of a gray colour, like ashes; others red, and others brown. They seem all to have been enclosed in leaden cases. Could it be proved that each letter was wrapped round with a thread, and that the thread, as in the seals affixed to diplomas, was drawn through the covering of the seal, the difficulty which I think occurs in the use of these earths, as mentioned by the ancients, would entirely disappear[356]. It seems to me remarkable that neither Theophrastus nor Pliny says anything of the Asiatic _creta_, or speaks at all of sealing-earth; though they have carefully enumerated all those kinds of earth which were worth notice on account of any use.