accumulating mud was briefly exposed to the air along tidal flats. Small phosphatic-shelled animals called brachiopods inhabited these tidal flats but as far as is known, nothing lived on land. Many shale beds are marked with faint trails and borings of worm-like creatures, and a few contain the remains of tiny trilobites. Covered by a shallow sea As the shoreline continued to move eastward, the 285-foot-thick (87 m) Death Canyon Limestone Member of the Gros Ventre Formation was laid down in clear water farther from shore. It consists of two thick beds of dark blue-gray limestone that are separated by 15 to 20 feet (4.5 to 6 m) of shale. The Death Canyon contains abundant fossil of brachiopods and trilobites in some places. Following this the sea retreated to the west for a short time. The 220-foot-thick (67 m) Park Shale Member of the Gros Ventre Formation was deposited in the shallow muddy water resulting from this retreat. It is a gray-green shale that contains beds of platy limestone conglomerate along with fossils of trilobites and brachiopods. Underwater expanses of algae flourished in places on the sea bottom and built extensive reefs. Periodically shoal areas were hit by violent storm waves that tore loose platy fragments of recently solidified limestone and swept them into nearby channels where they were buried and cemented into thin beds of jumbled fragments called 'edgewise' conglomerate. These are widespread in the shale and in overlying and underlying limestone layers. By Late Cambrian, the shoreline had once again crept eastward, resulting in clearer water that was probably 100 to 200 feet (30 to 60 m) deep. The 100-foot-thick (30 m) Gallatin Limestone was formed. It consists of blue-gray limestone that is mottled with irregular rusty or yellow patches. Interrupting the limestone are a few beds of 'edgewise' conglomerate that are indicative of sporadic storms. Now at its maximum extent, the sea covered all of Idaho, Montana, most of Wyoming and extended eastward across the Dakotas to connect with shallow seas that covered the eastern United States. Soon after, a slow uplift caused the sea to gradually retreat westward. The site of the Teton Range emerged above sea level, where, as far as is known, it may have been exposed to erosion for nearly 70 million years. Uplift puts the area back on the sea's edge The Ordovician Bighorn Dolomite forms ragged hard massive light-gray to white