A new zone, the Reticulatisporites carnosus Assemblage Zone of late Pendleian to Arnsbergian age, is proposed for miospore assemblages in the Searston Formation of the Barachois Group and in unnamed coal-bearing strata in higher portions of the group. The beds containing the zone can be correlated with those in other parts of the Euramerican floral province in western Europe (including the North Sea), where the climate was semi-humid. Temporal relationships suggested by these new biostratigraphic data indicate that a reassessment of the regional lithostratigraphy of southwestern Newfoundland is required. The Overfall Brook Member of the Robinsons River Formation, formerly assigned with its correlative, the Brow Pond Lentil, to the Codroy Group, is here identified as a basal unit of the Searston Formation. It lies unconformably on Codroy Group beds of Brigantian age. Elsewhere, the basal beds of the Barachois Group lie unconformably on pre-Carboniferous rocks. The Barachois Group in the Codroy and St. George’s Bay lowlands correlates with the Humber Falls and Howley formations of the Deer Lake Subbasin of western Newfoundland and with the Pomquet Formation of the Mabou Group, Nova Scotia. The Pendleian–Arnsbergian coal-bearing strata high in the undivided Barachois Group predate the post-Arnsbergian major floral crisis and, with their correlatives, represent the youngest known rock units of Mississippian age in Atlantic Canada. They are significantly older than the Pennsylvanian coal measures of Moscovian (Bolsovian) age in a small outlier near Stephenville, and we recommend the latter be removed from the Barachois Group.