You'll find stones like this everywhere, ripped out of mountains by the ice sheets that covered this land, transported back and forth as they moved, and then deposited when they melted. Sometimes they are obviously very different than the stone around them -- granite in limestone country, for example. These are in Tuamgraney, County Clare.
I am a journalist living in rural Ireland, and have written for the American Conservative, the Dallas Morning News, Front Porch Republic and other publications. I interview elderly Irish about traditional ways of life, and write a weekly column about the Long Emergency for my local newspaper.