Figure 6-70 Layers of Rock Laid Down by Water (a) This close-up image taken by the rover Opportunity shows a small section of rock layers in a location called the Dells. The angled and curved layering seen here is created only on Earth by water flow, strongly suggesting that this sediment was also deposited by water. The nearly spherical rocks, called “blueberries” because they are dark, have been chemically identified as hematite, an iron-rich mineral that is usually formed in water. The rovers have found blueberries strewn in a wide variety of locations. (b) This iron meteorite, dubbed the “Heat Shield Rock” because it was discovered behind the Mars rover Sojourner’s heat shield, is surrounded by hematite blueberries.