Ferricrete

Ferricrete is a hard, erosion-resistant layer of sedimentary rock, usually conglomerate or breccia, that has been cemented into a duricrust by iron oxides. The iron oxide cements are derived from the oxidation of percolating solutions of iron salts. Ferricretes form at or near the land surface and may contain non-local sediments that have been transported from outside the immediate area of the deposit.