I reckon this is one of those songs which either owes much to poetic licence or has simply been corrupted over the ages.

Apart from the Altan version, which Mairéad says she got from her late father Francie, there are two other recorded Donegal versions in Irish. The first is by Albert Fry (Belfast-born, but with strong Donegal connections) and the second by Caitlín Ní Dhomhnaill from Rannafast in The Rosses. Both versions were available on cassette from Cló Iar-Chonnachta (www.cic.ie).

As for geography, I don't think this song has anything to do with Mayo. The River Finn is in Donegal and meets the River Mourne south of Strabane. There is no River Finn in Mayo. Iorras is the Irish version of Erris in Mayo, but also of Urris in Inishowen.

That being said, there's no possibility that anyone could have stood on the banks of the Finn and 'been close to the waves' or watched big ships sailing into the ocean.

The Diarmúid and Gráinne reference is clearly a metaphor for emigration.

Lastly, 'rámha' does not mean 'thick'. The song's title loosely translates as 'island fort of the oars'. The island in question is impossible to identify.

I hope that helps, though it doesn't get you much further.