TRENTONIAN STAGE

division of Middle Ordovician time in North America (the Ordovician Period began about 500,000,000 years ago and lasted about 70,000,000 years); the Trentonian Stage is the uppermost stage of the Champlainian Series of rocks. Trentonian rocks consist largely of limestones and calcareous shales, although a notable black, graptolite-rich shale unit extends from New York to Alabama. The black shale interfingers with limestones to the east, and correlations must be made across the boundaries of these facies.