LANCE FORMATION

division of Late Cretaceous rocks in the western United States (the Cretaceous period began about 144 million years ago and ended 66.4 million years ago). Where it occurs, the Lance Formation is the uppermost rock unit of the Cretaceous. It was named for exposures studied near Lance Creek, Niobrara county, Wyoming. The Lance Formation varies in thickness from about 90 m (300 feet) in North Dakota to almost 600 m (2,000 feet) in parts of Wyoming and consists of grayish sandy shales, light-coloured sandstones, and thin lignite beds. It is well-known for its Late Cretaceous fossils, which include plants, dinosaurs, and mammals. The duckbilled dinosaur Trachodon, the great carnivore Tyrannosaurus, the herbivores Triceratops and Ankylosaurus, and mammals and marsupials have been found in the Lance.