Southampton Island in northern Hudson Bay has previously been considered to contain two Ordovician oil shale beds. These are within carbonate strata referred to as the Bad Cache Rapids and younger Churchill River Groups. The older shale, informally called "Boas River shale" was thought to occur between the groups. The younger, here informally named "Sixteen Mile Brook shale," is higher in the uppermost Churchill River Group at the Ordovician-Silurian boundary. Strong faunal evidence indicates that the Boas River is stratigraphically higher than previously thought and is probably coeval with the Sixteen Mile Brook shale. Thus, there appears to be only one shale bed although there is a possibility of a younger one within the Silurian. The Sixteen Mile Brook shale is about 5 ft (15 m) thick and extensive, having been traced at least 130 mi (208 km) and possibly up to 220 mi (352 km). Yields of nearly 45 gal (1.07 bbl) of oil per ton have been recorded. Total reserves of oil may approach or exceed 8 trillion gallons (30 billion cu m; 190 billion bbl).