​ACADIAN, in geology, the name given by Sir J. W. Dawson in 1867 to a series of black, red and green shales and slates, with dark grey limestones, which are well developed at St John, New Brunswick; Avalon in E. Newfoundland, and Braintree in E. Massachusetts. These rocks are of Middle Cambrian age and possess a Paradoxides fauna. They have been correlated with limestone beds in Tennessee, Alabama, central Nevada and British Columbia (St Stephen).