Figure 3d. Close-up of abrupt contact between gray and brown colored mud. Silty sand beds are seen marked by the rust color along the contact between sand and mud beds, best seen at the shovel handle and its head. The brown color is a pervasive stain, and like the rusty zones is a result of weathering by oxidation of iron-bearing minerals in the sand and mud.
Last updated on October 6, 2005