The Ste-Monique sill caps a number of small hills over an area of approximately 3x1 km. It is probably 6-7 m thick, although contacts are not exposed. The principal rock type consists of phenocrysts of augite, olivine, usually with margins of monticellite, and biotite in a groundmass of abundant poikilitic brown biotite, monticellite, calcite and accessory brookite, perovskite, apatite and opaques (Howard, 1922, pp. 61-8). Currie (1976a, p. 68) states that analcime and augite are the most abundant constituents, and that felsic ocelli are sometimes present.