From abstract: The Richey-Lambert coal field is an area of about 900 square miles in Richland and Dawson Counties, eastern Montana, along the divide between the Missouri and Yellowstone Rivers. In this region only flat-lying continental rocks occur near the surface. About 300 feet of the Lebo shale member and about 930 feet of the coal-bearing Tongue River member of the Fort Union formation, of Eocene age, are exposed in the area. Deposits of terrace gravel at two levels in the field are tentatively correlated with the gravel on the Cypress Hills, Saskatchewan, which has been assigned to the Oligocene by the Canada Geological Survey, and with the Flaxville gravel, of upper Miocene or Pliocene age.