There is a typescript among Sam Henry's papers which bears the words of a poem 'Mullaghcarn' which was written by one Albert Ernest Stafford Smyth of Hamilton Ontario and published in his volume "The Garden of the sun". However, it doesn't rhyme Mullaghcarn with fern.
It's a description of an idyllic day spent with his Norah.
To my mind it's a very minor poem, though Henry had a tune in tonic sol-fa (as he did). I'm loth to transcribe but will happily do, if it rings any further bells.
Looking further I see that Henry also had this as sheet music, published privately by Smyth. If there is point, I could forward a scan.