The name Mistamisk Formation was used by Dimroth (1972, 1978) to refer to a sequence of basalt and sedimentary rocks in the Mistamisk Lake area (sheet 24C08). This sequence is part of the Howse Lithotectonic Zone (Clark and Wares, 2004). According to Dimroth (1972, 1978), the unit extends northwards for at least 100 km (see e.g. Roscoe, 1957; Dressler, 1979). Near Mistamisk Lake, the Mistamisk Formation overlies the Bacchus Formation and consists of the same volcanic and sedimentary lithofacies, forcing Dimroth (1972, 1978) to arbitrarily set the lower limit of this formation. SW of Mistamisk Lake, the unit consists, from top to bottom, of: 1) >1500 m of massive and pillow basalt and interbedded graphitic shale, siltstone and impure sandstone; 2) ~30 m of laminated shale and siltstone; and 3) ~150 m of pillow basalt and interbedded graphitic shale, siltstone and impure sandstone (Dimroth, 1972, 1978). The upper sequence is cut by three gabbro sills with an overall thickness of 300 m. The middle sequence is cut by two or three gabbro sills. The top of the Mistamisk Formation is not present in the area mapped by Dimroth (1972, 1978). However, further north, the upper part of the Mistamisk Formation contains felsic pyroclastic layers (Dimroth, 1972, 1978; Dressler, 1979).

Dimroth (1972, 1978) considered three possibilities for the stratigraphic position of the Mistamisk Formation: 1) overlying the Bacchus Formation; 2) constituting the upper part of the Bacchus Formation; or 3) representing the upper part of the Menihek Formation. Dimroth favoured the third, while noting that the supporting evidence was very weak. In the Colombet Lake area, north of the area mapped by Dimroth (1972, 1978), the Mistamisk Formation was interpreted as overlying the Menihek Formation (Dressler, 1979). Clark and Wares (2004) proposed to assign rocks of the Mistamisk Formation to the Bacchus Formation.

The SIGÉOM interactive map indicates that all of the basalts referred to as Mistamisk by Dimroth (1972, 1978) and Dressler (1979) are assigned to the Bacchus Formation. The best evidence supporting this latter correlation is a zircon radiometric age of 2142 +4/-2 Ma (T. Krogh and B. Dressler, unpublished data cited by Clark, 1984, p. 34) obtained on a rhyolite dyke cutting the Mistamisk Formation, in the Colombet Lake area. Thus, the basalts cut by this dyke are older than 2142 Ma and cannot be correlated with the Menihek Formation, which is younger than 1878-1880 Ma, the age of the underlying Sokoman Formation (Chevé and Machado, 1988; Findlay et al., 1995). Basalts previously known as Mistamisk clearly belong to the first cycle of deposition in the Labrador Trough and were assigned to the Bacchus Formation, as proposed by Clark and Wares (2004). As the Mistamisk Formation is equivalent to part of the Bacchus Formation, the name Mistamisk Formation was abandoned, as recommended by Clark and Wares (2004).

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