From the familiar way in which the story of Oliver and Arthur is referred to, I suppose that it circulated in Ireland in 1772.  I know it only in a Spanish version, without date or printer's name, the title of which is,—"Historia de los muy Nobles y Valientes Cavalleros Oliveros de Castilla y Artus de Algarve, y de sus maravillosas y grandes hazañas. Compuesta por el Bachiller l'edro de la Floresta.  En Madrid, pp. 219."  In the time of Charlemagne, the King of Castille being left a widower with one son, Oliveros, married the Queen of Algarve, a widow with one son, Artus.  The boys were alike in person and disposition, and grew up friends.  The Queen formed an unlawful desire for Oliveros, who to avoid her importunities fled secretly, leaving a bottle for Artus, the liquid in which would be troubled should Oliveros be in danger.  Oliveros was shipwrecked on the coast of England, and after various adventures won the prize of a tournament, and the hand of Elena, the King's only child, who, the author carefully observes, was not Elena the wife of Menelaus, though not her inferior in beauty.  The tournament was unusually bloody, and among those slain was one of he Kings of Ireland.  The marriage was to take place at the end of the year, and Oliveros, to be near Elena, obtained the office of her grand carver, which he executed so as to excite universal admiration.  One day, being more attentive to her charms than his duties, he cut off one of his fingers, but concealed the hurt, and kept up the conversation.  The five kings of Ireland, to avenge the death of their fellow, invaded England.  Oliveros defeated and followed them to Ireland, which he conquered, and made the kings vassals to England.  One of these coming to do homage found Oliveros alone, having lost his way in pursuit of a boar.  He treacherously seized Oliveros, bound him hand and foot, and shut him up in a tower.  Artus finding the liquid in the bottle disturbed, knew that Oliveros was in difficulties, and set out to seek him.  While passing through a valley in Ireland, he was attacked by the monster:—

    "Y quiriendo ya salirse de aquel regno, entró en un valle muy grande, y de muy altos robles, y halló en él muchos animales, y en especial uno mayor que todos, que su vista era muy espantable, y tenia las narices, los dientes, y la boca, como un Leon.  Sus ojos parecian dos antorchas eucendidas, y el cuello tenia tres varas de largo; y á veces, le encogia tanto que juntaba la cabeza con sus hombros, y sacaba dos palmos de lengua, mas negra que el carbon, y por la boca hechaba tanto humo, que le cubria todo, y despues tendia el cuello quanto podia, y salia otro vez tanto humo, y daba grandes chillidos, y tenia los brazos gruesos y disformes; los pies tenia como de aguilla, tenia las alas muy grandes, á manera de alas de morcielago, y el otro medio cuerpo tenia como de sierpo; y la cola era tan grande como una lanza de armas; su cuerpo era como de corteza de roble, y duro como punta de diamante"—P. 144.

    Artus killed the monster, and rescued Oliveros.  Oliveros and Elena had a son and daughter.  Artus being seized by a horrible disease, dreamed that Oliveros could cure him, and Oliveros dreamed that the medicine was the life-blood of his children; so he cut off their heads, and restored Artus's health; and on going full of horror to Elena to confess what he had done, found them alive and well.  This miracle was proclaimed through London.  The son Henry grew up a valiant prince, but fell into the hands of the Turks and died in prison.  Artus married Clarissa, the daughter, and on the death of Oliveros and Elena succeeded to the thrones of Castile, England, and Ireland.
    By the usual rules of interpreting prophecies—keeping all that is like, leaving out all that is unlike, and twisting all that is doubtful—the monster is a very fair prefigure of a locomotive. H.B.C. (Notes and Queries, v.5, 1858)