Toarcian Stage

the uppermost stage (fourth from the bottom) of the Lower Jurassic. It was identified by the French paleontologist A. D. d’Orbigny in 1850. In its stratotype it is represented by bluish marls, 8–10 m thick, with intercalated argillaceous limestones. It is divided into three substages and six zones. The index ammonites are the Dactilioceratidae, Harpoceratinae, Hildoceratinae, and Grammoceratinae.