REPORT OF TEE CHIEF ASTRONOMER 129 



SESSIONAL PAPER No. 25a 



Western Phase. — The thickness of the formation as exposed in the Moyie 

 .-and Yahk ranges was roughly measured at two sections nearly along the Bound- 

 ary slash on the two sides of the Moyie river. One measurement gave approxi- 

 mately 8,000 feet; the other, 7,400 feet. In neither case was the base or top 

 of the formation actually visible. In a section still farther west both base and 

 top can be found in a nearly complete section of the Purcell series, but the 

 poor exposures in the dense forest cap there conspire with the difficulties of 

 mensuration, in an area of variable dips, to prevent a trustworthy measure- 

 ment of total thickness. This third section has, however, offered sufficient data 

 to render it probable that in the two former sections we have nearly the whole 

 thickness represented. The smaller of the two estimates, 7,400 feet, was won 

 from the structurally very favourable section in the fault-block bearing the 

 great Moyie sills at the Boundary line and immediately west of those sills. It is 

 possible, however, that even this lower estimate is too high and that the true 

 thickness might be more accurately placed at 7,000 feet. It appears certain 

 only that the Kitchener in this area cannot be less than 6,500 feet thick or 

 much more than 8,000 feet thick. For the present the original estimate of 

 7,400 feet may be accepted with the understanding ihat it may be several 

 hundreds of feet too great. 



The dominant rock of the western phase is to be classed as a notably 

 uniform quartzite. The bedding is, on the average, considerably thinner 

 than in the typical Creston quartzite. Individual strata range from 

 a minute fraction of an inch to six feet or more in thickness. A 

 few whitish beds, up to twenty feet thick, were observed at various horizons, 

 but they are rare. The average thickness of the individual bed seems to be 

 about three inches. As in the Creston formation, many of the thinner strata 

 may be grouped into strong, non-fissile plates several feet thick. The rock is 

 regularly gray or greenish-gray on the fresh fracture, this tint being normally 

 darker than that of fresh Creston quartzite. The weathered surface is strong 

 rusty-brown, in characteristic contrast to the older quartzite. Cross-bedding, 

 ripple-marks, and sun-cracks were seen at various horizons in both the quartzite 

 and interbedded metargillite, but these features are not so common as in the 

 overlying Moyie formation. 



Microscopic study shows that from 50 to 75 or 80 per cent of the dominant 

 quartzite is composed of grains of glassy quartz. The other essential constitu- 

 ents are the feldspars, including sodiferous orthoclase, microperthite, and pro- 

 bably untwinned albite; a variable but generally abundant quantity of sericite, 

 "biotite, and possibly paragonite. Secondary epidote and kaolin, along with 

 magnetite, pyrite, zircon, and apatite grains are minor constituents. The rusty 

 colour of the rock is due, not so much to the alteration of magnetite or pyrite 

 as to the freeing of iron oxide from the weathering micas. The essential con- 

 stituents are interlocked after the same thorough fashion observed in thin 

 -sections of the Creston quartzite. The grain of the rock is always fine, the 

 ravexage diameters of the quartz individuals varying, in different specimens 



25a — vol. ii — 9 



