The identification of Avallon with Glastonbury is probably post-pagan, and the names applied to Glastonbury--Avallon, _Insula Pomonum_, _Insula vitrea_--may be primitive names of Elysium. William of Malmesbury derives _Insula Pomonum_ in its application to Glastonbury from a native name _Insula Avallonioe_, which he connects with the Brythonic _avalla_, "apples," because Glastenig found an apple tree there.[1253] The name may thus have been connected with marvellous apple trees, like those of the Irish Elysium. But he also suggests that it may be derived from the name of Avalloc, living there with his daughters. Avalloc is evidently the "Rex Avallon" (Avallach) to whose palace Arthur was carried and healed by the _regia virgo_.[1254] He may therefore have been a mythic lord of Elysium, and his daughters would correspond to the maidens of the isle. William also derives "Glastonbury" from the name of an eponymous founder Glastenig, or from its native name _Ynesuuitron_, "Glass Island." This name reappears in Chretien's _Eric_ in the form "l'isle de verre." Giraldus explains the name from the glassy waters around Glastonbury, but it may be an early name of Elysium.[1255] Glass must have appealed to the imagination of Celt, Teuton, and Slav, for we hear of Merlin's glass house, a glass fort discovered by Arthur, a glass tower attacked by the Milesians, Etain's glass _grianan_, and a boat of glass which conveyed Connla to Elysium. In Teutonic and Slavonic myth and _Märchen_, glass mountains, on which dwell mysterious personages, frequently occur.