Late Silurian subtidal, interidal, and supratidal rocks are widely and complexly associated along the north coast of Somerset Island. The Read Bay Formation in the northwest, a subtidal limestone facies with brachiopod–coral faunas, is at least in part the lateral equivalent to the Leopold Formation in the northeast, the latter being an intertidal–supratidal facies of predominantly unfossiliferous dolomitic and sandy carbonate rocks. In intervening areas, the two fades intercalate widely, resulting in sections in which both subtidal and intertidal–supratidal sequences alternate repeatedly. The latter have been referred provisionally to the Read Bay Formation, although subsequent work may justify the designation of new lithostratigraphic units in the area of intercalation.The intertidal–supratidal rocks contain considerable quantities of texturally and mineralogically immature, sand-sized, detrital quartz, feldspar, and mica, apparently derived from nearby. The subtidal rocks also commonly contain large amounts (up to 50%) of clay- to silt-sized quartz, dolomite, muscovite, and clay minerals. The detrital sediment and the close association of subtidal and intertidal–supratidal rocks suggest that these Late Silurian rocks are part of a basin–margin succession flanking a low-lying land mass situated to the north and northeast. A general increase in the proportion of detrital sediment and greater persistence of near-shore carbonate facies toward the east suggest either greater proximity to a shoreline or a more persistently elevated land area in that direction.