The lyrics of “Morning Is Broken” (which, by the way, I like — you don’t have to sing the song syrupy, you know!) are of course by Eleanor Farjeon, a very gifted minor mid-century American poet. She was also the author of some very good fantasy books, mostly for children. I don’t know whether or not Farjeon was Catholic, but our parochial school library certainly included both her books and poems.
The music to which the lyrics are set is a 19th century Highland tune. Its composer is unknown, but it was used as the setting for “Leanabh an Aigh” (Child of Wonder), a Gaelic Christmas carol written by a poet from the island of Mull, Mary Macdonald, or to give her her full Gaelic name, “Mairi Dhughallach NicLucais, bean Neil Dhomhnullaich ann an Ard Tunna”. Which means, Mairi Dhughallach (Dhugallach’s her nickname, distinguishing her from all the other Marys), daughter of Lucas, wife of Neil Dhomhnullaich, from Ard Tunna. She would have been one of the clan of the MacDonalds, but she wouldn’t use that as a last name. (And not much point, really, given that practically everybody else thereabouts was a MacDonald, too!) The tune is called “Bunessan” (or Bun Easain for the Gaelic-ly correct) after a nearby village on Mull.
(UPDATE: Here’s a gorgeous picture of sunset at Bunessan.)
“Leanabh an Aigh” is apparently found in English hymnbooks in a translation called “Child in a Manger” and done by Lachlan MacBean (for his 1888 book Songs and Hymns of the Scottish Highlands) . This is apparently where Cat Stevens heard the tune.
As with most folk hymns, there are at least two slightly different versions of the Gaelic lyrics to “Leanabh an Aigh”. This one is online at Let’s Sing and is more complete, but also more “grammatically correct”. Which way Mairi actually sang it is anybody’s guess. There’s a shorter version online at this Esperanto site, believe it or not! The English translation is not by me and is not the same as “Child in a Manger”. I found two online translations called “Infant of Wonder”. One is by Hilda Leslie and was done in 1978. The other I found in the church history of Cambuslang Baptist Church. It was done by a former minister of the church, the Rev. D. Gunn Sutherland, back in the late 19th century. (Unfortunately, the church transcription left out the last line of the song!) Anyway, I’m doing a baaaad thing and combining the translations to better fit the Gaelic verses we have here, as well as making picky little changes which I’ve asterisked.