REPORT OF THE CHIEF ASTRONOMER 27 1 



SESSIONAL PAPER No. 25a 



MacDonald mentions an important group of metamorphosed and highly 

 crystalline sediments, now schists, outcropping" along the west shore of Coeur 

 d'Alene lake.§ This locality is about 120 miles due south of the area of the 

 Priest River terrane as mapped for the present report. It seems possible that 

 the one terrane is a continuation of the other. 



King recognized a greatly deformed series of slates, quartzites, limestones, 

 dolomites, mica schists, and hornblende schists in the ' Archean ' division of 

 the rocks encountered during the Fortieth Parallel survey.f Farther South 

 the quartzites and micaceous schists of the Vishnu group in the Grand 

 Canyon section represent other pre-Cambrian sediments which have suffered, 

 apparently, about the same measure of deformation and metamorphism as those 

 characterizing the Priest Eiver terrane. 



In British Columbia, north of the Boundary belt, it is fully as difficult 

 as in the cases already noted, to correlate with confidence. Among the des- 

 cribed rock-groups, the nearest approach, lithologically, to the Priest River 

 terrane is the Nisconlith series of Dawson, as exposed around the Shuswap 

 lakes.:}: This series is made up of calcareous or graphitic mica schists, flaggy, 

 often dark-coloured limestones, gray and blackish quartzites in apparent con- 

 formity. The series appears to lie conformably beneath the Adams Lake 

 series and both are placed in the Cambrian, the Nisconlith overlying the truly 

 Archean Shuswap series of gneisses, etc. All three series are quite unfossili- 

 ferous and the present writer suspects that the correlation of the Nisconlith 

 with the Priest River terrane is at least as justifiable as that with the Cam- 

 brian of the Front ranges. 



The foregoing brief statement of the constitution and relations of the 

 various groups indicates lines of thought in the future correlation of the ancient 

 formations of the Cordillera, rather than any definite view as to the correlation. 

 One thing is certain, however; the Cordillera is at many points underlain by 

 very thick and important groups of sediments which are not only pre-Cambrian 

 but also pre-Beltian in age. It is possible if not, indeed, probable that the 

 total thicknesses of these stratified rocks rival those of the pre-Cambrian 

 terranes in the Great Lakes region of Canada and the United States, as well 

 as those of the vast formations of Finland. 



Pend D'Oreille Group. 



General Description. — Between the western limit of the Summit series 

 monocline and the southeastern edge of the great central volcanic field, an 

 area of about sixty square miles of the ten-mile belt is underlain by a thick 

 group of unfossiliferous, heavily metamorphosed sediments. A considerable 



$ D. F. MacDonald, Bull. 285, U.S. Geol. Survey, 1906, d. 42. 



t Report, Vol. 1, Systematic Geology, 1878, p. 532 



t G. M. Dawson, Explanatory notes to Shuswap sheet, Geological Survey of Can- 

 ada, 1898. For further references see Bull. Geol. Soc. America, Vol. 12, 1901, p. 66. 

 Since this report went to press, the writer has proved the pre-Beltian age of the Niscon- 

 lith of the Shuswap district. 



