The rocks on Mars offer all the intriguing clues of a good mystery novel for principal investigator Steve Squyres. “Some of them mean something,” the Cornell University scientist said Monday. “Some of them are probably red herrings. We don’t know which is which.” NASA’s rover Spirit ground a circular hole in the rock called Adirondack and verified its volcanic origins. Even more intriguing, Opportunity, on the other side of Mars, has found fine layers of rock that could be caused by volcanic ash or dust.