The Oldman and Foremost formations comprise an easily recognizable stratigraphic unit in Southern Alberta because of their lithologic character and position between marine strata. The Oldman is a continental type of deposit consisting essentially of light gray sandstones and gray shales. The Foremost formation underlies the Oldman conformably, and is brackish-water in origin. It is composed of sandstones, silts, shales of darker hues than those of the Oldman, and coal seams. These formations were laid down at or near the margins of the Bearpaw and Pakowki seas; hence, marine phases occur in the Foremost, and brackish-water phases in the Oldman. Thickness of the combined formations varies from 1,600 feet near the southwestern foothills to 600 feet in the eastern part of Alberta.