Áine,
There is a wealth of trad Irish songs pre 1870, in english. Barry Gleeson recorded a beauty on the CD "The Croppies Complaint" released in commemmoration of the 1798 rising. It was written by a Dublin loyalist of the time William Ball. All of his compositions are in a Dublin museum now.
But there were loads more. As you travel from East to West so the songs of pre 1870 are either translations from Irish or are still sung in Irish and a lot are beautiful. That does not mean that songs in English were not beautiful or well written.
I am never more amazed than when I hear versions of songs still being sung in rural parishes. Some of the songs penned many , many years ago.
The Tradition is still alive here in Ireland.