The Eltdown Shards are bizarre fragments of seeming pottery found in 1882 and named after Eltdown in southern England, where they were first discovered. These shards date to the early Triassic period. Previously believed to be untranslatable, there have been several "translations" made, such as The Eltdown Shards: A Partial Translation, by Gordon Whitney. There are also a variety of non-collegiate translation, most of which make the rounds among cults.
The translation by Whitney is similar to another text, the Pnakotic Manuscripts, produced by the archaeosapients currently termed Yithians, which describes the planet Yith and the first encounters with the Yekubians. There also appears to be a shard that contains the formula for summoning a being known as the "Warder of Knowledge." It should be noted that the formula for dismissing the Warder is either not present or intentionally damaged. However, the majority of information contained on the shards deals with shoggoths, and may or may not make vague references to some sort of "prime source," which means that it's more likely the shards were inscribed by the Elder Things.