Looking for relatives in Ireland

Greetings. I am attempting to trace back my family genealogy to the UK, specifically Ireland. My Grandfather, Frank Oliver Blake, was born in 1870 in Vermont, USA.

His parents were (supposedly) Frank ( or George) Blake and Anna (Flannery) Blake. They would have immigrated around the time of the Potato Famine. Maybe born in 1840's and married in Ireland or England.

I cannot find any trace of a Birth Certificate for my Grandfather nor any specific immigration records or passenger lists. However, his Marriage Licenses list them as such from Ireland.

They may have immigrated first through HighTower, London, England.

Any assistance is welcome and appreciated.

Regards,

George