The "Discovery Scarp"

Caption NASA originale:"One of the most prominent lobate scarps (Discovery Scarp), photographed by Mariner 10 during it's first encounter with Mercury, is located at the center of this image (extending from the top to near bottom). This scarp is about 350 Km long and transects two craters 35 and 55 Km in diameter. The maximum height of the scarp south of the 55-Km crater is about 3 Km. Notice the shallow older crater (near the center of the image) perched on the crest of the scarp. (FDS 17389 and 27399)".