The Mabou-Inverness coal-bearing section is exposed along the shores of small land areas that form part of the large Carboniferous Basin beneath the Gulf of St. Lawrence. The Westphalian C and D section measures 930 m and contains 26 seams that are 0.3-3.8 m thick. The coals have a rank of high volatile ＇＇B＇＇ to high volatile ＇＇C＇＇ bituminous, with vitrinite reflectance values of 0.6-0.7% R(max). Petrographic composition, in terms of microlithotypes and macerals, was determined on column samples of thirteen seams, and is illustrated in percentage diagrams. A normal banded humic coal is indicated in which the bright-banded variety predominates. Average ash, sulphur and volatile matter contents are, respectively, 12.4%, 3.7% and 39% (on mineral matter-free basis). Coal facies has been determined from the microlithotypes and is expressed in terms of forest moor (FM), reed moor (RM) and open moor (OM). In addition, whole-seam facies designations are given also and are compared with those of the Sydney, Port Hood and St. Rose coalfields. They show that at Mabou Mines the RM facies greatly predominates, but at Inverness the FM facies is the dominant feature, as is the case at Sydney, while at Port Hood OM conditions prevailed. Higher paleo-groundwater tables at Mabou Mines and Port Hood are deduced from this and are supported by the presence of Anthracomya-bearing black shales. Maceral-based facies plots suggest that the Mabou coals originated in the piedmont zone of the Hercynean foreland region, possibly in a southern embayment bordered by upland areas. Further north, however, in the Inverness area, the coal swamps may have extended uninterrupted to the Sydney field and may have covered the pre-Carboniferous Cape Breton Highlands before their uplift in Early Permian time.