REPORT OF THE CHIEF ASTRONOMER 103 



SESSIONAL PAPER No. 25a 



Insoluble in hydrochloric acid 74-08% 



Soluble in hydrochloric acid: 



Fe 2 O s 6-62 



AiA 5-96 



CaO 9.70 



MgO 3-64 



The strong 1 ' deficit ' in carl on dioxide and the great abundance of combined 

 water leads one to suspect that the magnesium may be present in the form of 

 the basic carbonate or in the form of a hydrous magnesium silicate, or possibly 

 In both forms. The analysis evidently does not lend itself to useful calcul- 

 ation. The rock has the chemical composition of a somewhat dolomitic argillite, 

 "which is high in silica and iron oxides, and low in alumina. 



Wigwam Formation. 



The AlacDonald formation is succeeded above by the Wigwam formation, 

 named from the river which receives part of the drainage of these mountains. 

 On reference to the map sheet, it will be seen that a band of rocks referred to 

 the subdivision follows a long, high ridge running south from the Boundary line 

 at a point half-way between the Kootenay and Flathead rivers. A second 

 •extensive, though less perfect exposure of the Wigwam occurs about six miles 

 to the eastward. Elsewhere in the belt these rocks have either been eroded away 

 or lie buried beneath the Siyeh formation. The total thickness was measured 

 in the more westerly band and was found to be about 1,200 feet. 



The Wigwam formation consists of a mass of fairly homogeneous red or 

 brownish-red sandstones, interrupted by partings of red, silicious metargillite. 

 Though the bedding is generally thin, the sandstones are often united into platy 

 aggregates one to three or more feet in thickness. A few gray or brown-rusty 

 metargillite beds and some red gritty layers form subordinate intercalations. 

 Throughout the formation sun-cracked and ripple-marked, sometimes cross- 

 bedded, horizons occur. A few markings, interpreted as annelide burrows, 

 were seen, but no more useful fossils were discovered. These red beds are rather 

 sharply defined against the gray or light brownish strata of the overlying Siyeh, 

 which is, however, perfectly conformable. As already noted, the Wigwam 

 and ATacDonald rocks are dovetailed together through interbedd'ing. 



The principal phase of the formation is a fine-grained sandstone, charged 

 with a variable amount of ferruginous and once-argillaceous cement. Its 

 essential constituents are quartz, in rounded and angular grains; abundant 

 subangular grains of orthoclase, microperthite, microcline, and plagioclase 

 (near andesine Ab^Anj) ; and generally-rounded grains of a ferruginous chert. 

 The iron ore, probably hematite, is relatively abundant; it is finely divided and 

 generally opaque. Kaolin and sericite are extensively developed. A few 

 clastic zircon? were observed under the microscope. The sericite is especially 

 developed in the non-argillaceous beds and in the bedding planes. Rarely the 

 grains of quartz show enlargement with new silica. On the whole the rock 

 preserves the eminently clastic structure of true sandstone and it cannot fairly 

 be called a quartzite. On the other hand, the never-failing generation of 



