Used from the 5th through 10th centuries, known mainly from stone memorials but known to have also been used on message sticks. The straight lines make this alphabet optimized for carving: Wikipedia shows the complete forms. Tradition ascribes the names of letters to trees, but this is disputed, and thanks to Robert Graves's interpretations in The White Goddess, the past couple generations' of scholarly battles over this have been quite entertaining (as long as you manage to keep your distance). The name for these letter was borrowed in the 1620s from Irish, where its origin is uncertain but traditionally associated with Ogma, the legendary inventor of this alphabet.
The ruined church has a beautiful round tower, a holy well, a primitive oratory, and a couple pillar stones inscribed in ogham.