These are Richard Hook illustrations from Great Folk Tales of Old Ireland, compiled by Mary Mary McGarry in 1972. I didn’t find a lot of information about Richard Hook, just that he was a free lance illustrator, 1938-2010. From what I can tell, these are extremely different from his usual illustrations, and by far the most interesting and beautiful to me. So different that I wonder if maybe this is a different Richard Hook who illustrated books at the exact same time… Though that seems very unlikely. He worked primarily for Osprey Books, you can read a very loving remembrance of him on their website.