Petrogylphs are carved into rock. I can do a painting of a petroglyph, but if I painted on a rock it would be a rock painting, underground it would be a cave painting. What did I learn checking to make sure my own understanding was correct? What a morpheme is. It is the smallest part of a word that has meaning. Like 'un' as in unlikely, meaning not likely, or 'im' as in imperfect. But not 'very' as in very unique, because there is no such thing. Unique means one of a kind and you either is or you isn't. There ain't no 'very' about it.
Now, of course, well not now as in now, but later, I will have to see if I can paint a painting of a petroglyph. On canvas paper or the like.