(after the city of Apt, France), the fifth stage from the bottom in the lower section of the Cretaceous system. It was distinguished by the French geologist A. D. d’Orbigny in 1842. In a typical area it is composed of clayey limestones and marls, with a transition to white zoogenic limestones. It is divided into two substages according to its content of ammonites: the Bedoul, with Hoplites deshaesi, and the Gargas, with Oppelia hisus. It is widely represented in France, England, and the Federal Republic of Germany. In the USSR it is found in the Volga area, the Crimea, the Caucasus, the Kopet-Dag, the Pamirs, and Siberia and on the Kamchatka Peninsula.
B. M. KELLER