Three formations of the Belt series—Prichard, Wallace, and Striped Peak—can be traced northward from the northeastern part of the Coeur d’Alene district, Idaho, through the Trout Creek quadrangle to the northern part of the Libby quadrangle, Montana.

The differences upon which the separation of the Burke, Revett, and St. Regis is based in the Coeur d’Alene district, however, become less definite northward and fail entirely beyond the Clark Fork. In the area under consideration, therefore, these three are grouped under the term Ravalli according to the usage adopted by Calkins.

Stratigraphic details of parts of the Ravalli group and the Wallace and Striped Peak formations are given in tabular sections. Certain beds of the Wallace in the Trout Creek quadrangle show “molar tooth” structures similar to those of the Siyeh and Kitchener formations along the international boundary. In the Libby quadrangle both the Wallace and the Striped Peak contain beds of dolomitic limestone showing fossil algal forms similar to those in Glacier National Park.

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