Eagle Formation (Ke): Gray or grayish brown, thick-bedded sandstone, sandy shale, and thin interbedded coal. Chert-pebble lag deposit common at top of formation. Virgelle Member (lower part of formation in parts of central Montana): very light gray, gray, or brown sandstone that coarsens upward. Root zone and thin carbonaceous beds at top of member. Delta, coastal plain, tidal flat, and marine shoreface and foreshore. Thickness as much as 150 m (492 ft). Telegraph Creek Formation (Ktc): Thin interbeds of yellowish brown sandstone or siltstone and gray shale. Marine shoreface and offshore. Thickness as much as 200 m (656 ft).