Lower Jurassic. It was identified at the end of the 18th century by the English engineer W. Smith in Somersetshire (Great Britain). A typical section consists of regularly alternating flaglike limestones and argillites. The Liassic is divided into six stages—Hettangian, Sinemurian, Lotharingian, Pliensbachian, Domerian, and Toarcian—and is characterized by ammonites. Sediments were deposited almost everywhere during the age of regression of the sea and are represented chiefly by dark-colored sandy-argillaceous formations. Liassic deposits are known on virtually all continents. In the USSR, Liassic deposits are found in the Carpathians, the Crimea, the Caucasus, western Kazakhstan, and Eastern Siberia. Coal, oil, and gas deposits are associated with Liassic deposits.