A chert bed in this Formation is strikingly similar in petrography and inferred origin to Australian and South African silcretes. It occurs along an erosion surface that formed subaerially, and it contains colloform chalcedony and abundant ferruginous minerals. This chert also contains pseudomorphs and ghosts of halite. Silica precipitated from a solution that became enriched in electrolytes as a result of dissolving halite. Sand- size chert grains in the Whitehall are petrographically like the Whitehall silcrete and are probably grains of reworked silcrete.-Authors