In the _Four Ancient Books of Wales_, which are poetical compositions, whereas the _Mabinogion_ tales are prose with extremely little verse, there are certain interesting passages to illustrate the ancient Fairy-Faith of the Brythons from some of its purest sources. The first selected example comes from the _Black Book of Caermarthen_. It is a poem, sometimes called the _Avallenau_, from among the poems relating to the Battle of Arderydd; and it represents _Myrddin_ or Merlin, the famous magician of Arthur, quite at the mercy of sprites. The passage is an interesting one as showing that in the region where Merlin is supposed to be under the enchantment of the fairy woman Vivian he was regarded as no longer able to exercise his wonted control over spirits like fairies. As in ancient non-Celtic belief, where the loss of chastity in a magician, that is to say in one able to command certain orders of invisible beings, always leads to his falling under their lawless power, so was it with Merlin when overcome by Vivian. And this is Merlin's lamentation:-- Ten years and forty, as the toy of lawless ones, Have I been wandering in gloom among sprites. After wealth in abundance and entertaining minstrels, I have been [here so long that] it is useless for gloom and sprites to lead me astray.[318] In a dialogue between Myrddin and his sister Gwenddydd, contained in the _Red Book of Hergest I_,[319] there is a curious reference to ghosts of the mountain who, just like fairies that live in the mountains, steal away men's reason when they _strike_ them,--in death which may appear natural, in sickness, or in accident. And after his death--after he has been _taken_ by these ghosts of the mountain--Myrddin returns as a ghost and speaks from the grave a prophecy which 'the ghost of the mountain in Aber Carav'[320] told him. Not only do these passages prove the Celtic belief in ghosts like fairies to have existed anciently in Wales; but they show also that the recorded Fairy-Faith of the Brythons, like that of the Gaels of Ireland and Scotland, directly attests and confirms our Psychological Theory. Like a record from the official proceedings of the Psychical Research Society itself, they form one of the strongest proofs that fairies, ghosts, and shades were confused, all alike, in the mind of the Welsh poet, mingling together in that realm where mortals see with a new vision, and exist with a body invisible to us.