REPORT OF THE CHIEF ASTRONOMER 69 



SESSIONAL PAPER No. 25a 



through, dynamic metamorphism, it is a quartz-mica schist or a quartz-feldspar 

 schist or gneiss. If an argillite has been more or less completely recrystallized 

 by thermal action on igneous contacts it is a hornfels. If, finally, an argillite 

 retaining the bedding structure has been essentially recrystallized by deep 

 burial and without being affected by direct magmatic influence or by the 

 notable development of cleavage or schistosity, it may be called metargillite. 

 At no point within the Boundary belt was true argillite (shale or slate) 

 found in the Appekunny formation. Everywhere the once-pelitic phases belong 

 to the metargillite type as just defined. On the mountain slopes running up 

 eastward from the Flathead valley both metargillite and quartzite have been 

 sheared and cleaved, the former giving local phases of slaty metargillite. The 

 crystallinity never rises to the degree of true mica schist. 



Grinnell Formation. 



The Grinnell formation was named by Willis and described by him thus : — 



' A mass of red rocks of predominantly shaly argillaceous character 

 is termed the Grinnell argillite from its characteristic occurrence with a 

 thickness of about 1,800 feet in mount Grinnell. These beds are generally 

 ripple-marked, exhibit mud-cracks and the irregular surfaces of shallow 

 water deposits. They appear to vary considerably in thickness, the max- 

 imum measurement having been obtained in the typical locality, while 

 elsewhere to the north and northwest not more than 1,000 feet were found. 

 It is possible that more detailed stratigraphic study may develop the fact 

 that the Grinnell and Appekunny argillites are really phases of one great 

 formation, and that the line of distinction between them is one diagonal 

 to the stratification. The physical characters of the rocks closely resemble 

 those of the Chemung and Catskill of New York, and it is desirable 

 initially to recognize the possibility of their having similar interrelations. 



' The Grinnell argillite outcrops continuously along the eastern side 

 of Lewis range and its spurs, occurring above the Appekunny argillite and 

 dipping under the crest of the range at the heads of the great amphi- 

 theaters tributary to Swift Current valley. About the sources of the 

 Kennedy creeks it forms the ridge which divides them from Belly river. 

 Mount Robertson is a characteristic pyramidal summit composed of these 

 red argillites. The formation occurs in its proper stratigraphic position 

 between the forks of Belly river and west of that stream in the Mount 

 "\Vil?on range of the Canadian geologists, the northernmost extremity of 

 the Lewis range; and it dips westward under the valley of Little Kootna 

 creek and Waterton lake. On the western side of Livingston [Clarke] 

 range the Grinnell argillite was recognized as a more silicious, less con- 

 spicuously red or shaly division of the system, occurring about Upper 

 Kintla lake.'* 



* B. Willis, Bull. Geol. Soc. America, Vol. 13, 1902, p. 322. 



