Well I don’t think I’d call it art but I will say it was made by ancient man, we have something similar on the ranch. Early Americans would use slabs of abrasive stones to grind the edges on flint so it would be more durable when working. A raw flint edge will crush when struck but a ground edge will flake, and that’s what they want. Some of the rocks have grooves a foot long or more and they may go in any direction but they’re always straight.
These may be sharpening grooves for their spears and arrowheads..................