Rocks of Permo-Pennsylvanian age are chiefly confined to the Rocky Mountains where they consist of up to 700 feet of sandy dolomite, quartzitic and cherty sandstone and phosphate beds. In northern Alberta, in the Peace River area, a heterogeneous assemblage of sandstone, dolomite, chert and shale of comparable age attains a thickness of 900 feet. This thick development is related to the subsidiary Mississippian basin referred to above.
Triassic Triassic rocks occur mainly in the Rocky Mountains where they attain a thickness up to 3,000 feet.
They extend under the plains, only in the Peace River area of northern Alberta, forming a salient probably related to the above mentioned Mississi - Spray River formation, consists of dolomitic siltstones, fine gray sandstones and dark gray sandstones. The upper part includes dolomite, limestone, gypsum, anhydrite and associated red beds. Natural gas in commercial quantity and some oil shows have been found in Triassic siltstones of the Peace River area. pian basin. The lower part of the series, called t K e Jurassic Lower, Middle and Upper Jurassic sediments up to 1,500 feet in thickness occur in the western mountains and foothills. There they overlie Triassic, Pennsylvanian or Mississippian, and extend far out over the Peace River plains in northern Alberta and across the southern parts of Alberta, Saskatchewan and Manitoba but they are absent through non-deposition or erosion over central Alberta. In the foothills, the sediments are predominantly dark marine shales, grading upwards into brown marine sandstones. The marine sandstones in turn pass upwards into nonmarine sandstones and carbonaceous shales which have been referred to both Jurassic and Cretaceous.
In southern Alberta, the Jurassic consists of three parts: a lower part of sandstone and shale; a middle part of gray shale and limestone, and an upper of glauconitic shales with chert pebbles and rib on sandstones. In southern Saskatchewan and southwestern Manitoba, the Jurassic has three recognizable divisions: a lower evaporite; a middle shale and oolitic limestone, and an upper shale and sandstone division. ' %art Cretaceous Cretaceous sediments are distributed over the entire plains area except in the Northwest Territories where they occur only s oradically. These sediments foothills and mountains and thin progressively towards the Basement Complex due to depositional thinning and truncation. The boundary between the Lower and Upper Cretaceous has not been everywhere satisfactorily established. For convenience the deposits are described in three parts: in the foothills and mountains, the lower part consists mostly of non-marine conglomerates and sandstones and carbonaceous shales with coal beds; t