REPORT OF THE CHIEF ASTRONOMER 105 



SESSIONAL PAPER No. 25a 



SOO feet. — Kocks like those of the upper division but without red beds or gray lime- 

 stone; chiefly medium-bedded to thin-bedded green and greenish-gray, 

 highly silicious, sometimes dolomitic metargillite, weathering light 

 brown and, less often, gray. Many sun-cracke and some ripple-marks 

 occur at various horizons. 



4,000 feet. 



Base, conformable top of the Wigwam formation. 



The strong chemical contrast between the middle member and either of 

 the other two members might suggest the inadvisability of grouping all those 

 rocks in one formation. The grouping has been made partly in the interests of 

 correlation, partly on the ground that throughout the whole 4,000 feet of thick- 

 ness the strata show nearly uniform compactness and character of bedding and 

 fairly constant colour in both fresh and weathered phases, so that, in the field, 

 it is not easy to distinguish the metargillite from the often highly argillaceous 

 limestone. 



There is nothing specially novel in the detailed characters of the upper 

 and lower members but certain noteworthy conclusions follow from the facts 

 derived from the microscopic and chemical examination of the limestone in 

 the middle member. A close study has been made of type specimens collected 

 on the spur just west of the cascade on Phillips creek, near Roosville post 

 office. In colour, character of bedding, and other microscopic character, these 

 rocks are essentially similar to the typical Siyeh limestone of the Clarke and 

 Lewis ranges. They show the molar-tooth structure in notable perfection. 

 (Plate 14, A) . Not only the calcific lenses and pencils but also the buff -weather- 

 ing magnesian parts effervesce with cold dilute acid. 



The calcitic partings have microscopic characters identical with those of 

 the partings in the molar-tooth rock of the Clarke range; each is made up of 

 aggregated granules of calcium carbonate averaging 0-02 mm. in diameter. 

 Scarcely a grain of another substance is to be seen in these parts of the thin 

 sections. 



The magnesian parts are, on the other hand, quite highly composite. The 

 pale brownish, often rhombohedral crystals of dolomite or magnesian calcite 

 are distributed through an abundant matrix of quartz, feldspar, sericite, chlorite, 

 and a thin cloud of black dust- particles, partly magnetite and partly carbon. 

 The rhombohedral grains average about 0-02 mm. in diameter; the anhedral 

 carbonate grains may be considerably smaller. The grain of the matrix is very 

 fine, the quartz particles not surpassing the carbonate grains in average size. 

 The feldspars are too small for specific determination and are recognized as 

 such by their polarization tints, checked by the chemical analysis of the rock. 

 Sericite (also paragonite?) is relatively abundant. Original argillaceous 

 material cannot be demonstrated in the thin section; its recrystallization in 

 the form of sericite, chlorite, quartz, iron ore, and possibly feldspar seems to 

 be nearly perfect. 



A large, characteristic specimen (No. 1221) of the molar-tooth rock, which 

 wa3 collected just west of the Phillips creek cascade near Roosville post office, 

 was selected for chemical analysis. The difficulty of securing material carry- 



