Here's a version from Sam Henry's Songs of the People, which says the source is unknown.
-Joe Offer-

THE STRANDS OF MAGILLIGAN

I'm a stranger in this country, from America I came,
There's few in it knows me or can tell my name,
And here among strangers I will stay for a while,
For the sake of my darling I'll go many a long mile.

The strands of Magililgan divide in two parts
Where young men and maidens they meet their sweethearts,
They will take no denial, we must frolic and sing
And the sound of the fiddle, oh, it makes my heart ring.

On the top of a cuff where her castle does stand,
It is well built, with ivy down to the back strand
It is well built, with ivy and diamonds so bright,
It's a pilot for sailors on a dark stormy night.

On Magilligan top where the wild birds do fly,
There is one amongst them that flies very high,
On eagle's wings soaring, I'll speed as the wind,
The wild deep exploring, my true love I'll find.

The strands of Magilligan divide in two parts
And rejoin, as in dancing do lads their sweethearts,
So the strands, bright and shining, tho' parted in twain,
Reunite like two lovers where the Foyle meets the Main.

Notes: versions of this song vary greatly - there are almost as many titles as versions.