their type areas refer to Sutherland Brown (1963) for the Isaac Formation and to Campbell et al. (1973) for the entire Cariboo Group. Lithological descriptions of the formations in the following discussions are compiled from incomplete sections within the map area. Isaac Formation The Isaac Formation consists of phyllite, calcareous phyllite, limestone and minor quartzite. The thin-bedded marly layering and carbonate content of the phyllite is characteristic of the unit. The calcareous phyllite distin- guishes it from the Dome Creek Formation which also has interbedded limestone and phyllite. Isaac Formation pelite is more calcareous than the Black Stuart Group and the pelite is generally less siliceous. Isaac Formation occurs on the east slopes of Kimball Ridge extending into the valley of Matthew River, in the valley of Lostway Creek and north of Separation Creek. The type area of the Isaac Formation is along the east side of Isaac Lake in the Cariboo Mountains. It was first described by Sutherland Brown (1963) and later by Young (Young, 1969; in Campbell et al., 1973). Within the map area, Mansy (1970) described Isaac Formation at Kimball Ridge. The formation is thickest (approximately 1000 m) in the Matthew River area and may thin westward. Although the base of the Isaac Formation near Mount Kimball is not seen, the upper contact with the Cunning- ham Formation is gradational. The gradational interval involves thinning of the phyllite beds and thickening and lightening in colour of the limestone. The top of the Isaac Formation is placed at the dark brown weathering dark grey micritic limestone which is interbedded with black phyllite in near equal proportions beneath the massive thick carbonate of the Cunningham Formation. The base of the Cunningham Formation has 3 to 5 cm beds of grey micritic limestone separated by lamellae of black phyllite (0.5 cm or less). Approximately 8 m of the base of the Cunningham Formation and some 120 m of the upper part of the Isaac Formation define the gradational interval. For another 250 m downsection steel-blue weathering black to dark grey phyllite is interbedded with 2 to 6 cm calcareous brown weathering phyllite and minor brown weathering dark grey micritic limestone. The phyllite con- tains porphyroblasts (2 to 4 cm) of pyrite and ankerite. Scattered outcrops downsection from Kimball Ridge and extending into Matthew River valley consist of the same lithology but with occasional beds of grey limestone (3 to 10 m thick). In the valley calcareous phyllite with marly laminae (1 to 5 cm) is typical of the type section on Isaac Lake. Associated with the phyllite and calcare- ous phyllite are rare 1 to 2 m beds of moderate to coarse grained greenish-grey micaceous quartzite. The section on Kimball Ridge is more carbonate-rich than that at Isaac Lake. Campbell et al. (1973, p. 34) reported that the Isaac Formation becomes more calcareous westward from the Rocky Mountain Trench where it consists of phyllite, siltstone and minor sandstone directly below the Cunning- ham Formation. The increase in limestone content west- ward is confirmed by the Matthew River-Kimball Ridge exposures. Age and correlation. Young (1969 and in Campbell et al., 1973) correlated the Isaac Formation with the upper Miette Group of the Rocky Mountains because of simi- lar lithology and thickness and both units overlie litho- logically similar rocks, the Kaza Group and Middle Miette Group, respectively. The Isaac Formation, like the Upper Miette, is considered upper Proterozoic (Young, 1969). No evidence has been found to either substantiate or refute this correlation. The calcareous phyllite of the Matthew River-Mount Kimball area is most certainly Isaac Formation and can therefore be correlated with occurrences of that formation in the Cariboo Mountains to the east. Cunningham Formation The Cunningham Formation consists of limestone, dolo- stone marble and minor phyllite. In solitary outcrops the carbonate is easily mistaken for parts of the Isaac or Mural formations. In more continuous exposures the Cunningham can be distinguished from the Mural For- mation by more common interleaving of black carbona- ceous phyllite in its lower sections and by being grada- tional with both the underlying Isaac and overlying Yankee Belle formations. The Mural Formation is in sharp contact with bounding units. Cunningham Formation underlies much of the area east of Pleasant Valley Thrust. However, it is everywhere incompletely exposed due either to overburden or struc- tural disruption. The type section for the Cunningham Formation is’ defined as the reference section described by Campbell et al. (1973) to the northeast at Haggen Creek, Cariboo Mountains. That section is complete and represents the present concept of the Cunningham Formation. The type section originally defined by Holland (1954) near Round- top Mountain is incomplete and contains rocks other than Cunningham Formation. At the reference locality the Cunningham Formation consists entirely of limestone except for minor grey shale near its lower contact with the Isaac Formation. Young (in Campbell et al., 1973) pointed out that west and east of this section the Cunningham Formation includes shale, siltstone and sandstone whereas to the east near the Rocky Mountain Trench it is primarily dolostone. He reported the Cunningham Formation to be thickest (550 m) at Haggen Creek. Thicknesses of the Cunningham Forma- tion in the map area are: 360 m; Kimball Ridge 640 m;_ south of Separation Creek and just north of Little River 420 m;__ below the thrust fault that puts Cunningham 11