Duquette (1970) was the first to mention the Cummings Complex in its work. The Cummings Complex stratigraphy was established from underground work on the Opémiska property (McMillan, 1972), during surface mapping by Duquette (1982) and drilling in the Barlow Lake area (Poitras, 1984). Daigneault and Allard (1990) suggest modifying the original Cummings Complex name for Cummings Sills to meet the standards of the North American Stratigraphic Code (DV 86-02, sections 31 to 41). Leclerc et al. (2017) rather propose to change the name for the Cummings Intrusive Suite to include the following three formal lithodemes: (a) Roberge Sill, (b) Ventures Sill, and (c) Bourbeau Sill.

The Cummings Intrusive Suite consists of three differentiated sills that always appear in the same stratigraphic order (Duquette, 1982; Poitras, 1984; Bédard et al., 2009):

The Roberge Sill (nArob) includes a pyroxenitic zone with a gabbro chilled margin, a rhythmic zone composed of dunite, werhlite and clinopyroxenite with sheared, mylonitized and serpentinized contacts and a sommital dunitic zone in direct contact with the host rock, without showing a chilled margin.

The Ventures Sill (nAven) includes a zone of dark green clinopyroxenite with mesocumulate-adcumulate texture, a zone of foliated gabbro and ophitic gabbro, and a granophyre zone. Granophyre is characterized by a dominant myrmekitic texture with a dioritic border in the first few metres.

The Bourbeau Sill (nAbou) consists of a thin layer of basal bronzite-clinopyroxene pyroxenite, overlaid by massive subophitic leucogabbro and a large amount of ferrodiorite and quartz ferrogabbro.