REPORT OF THE CHIEF ASTRONOMER 135 



SESSIONAL PAPER No. 25a 



2-65S — 2-773) is 2-710. This value indicates the .admixture of the less dense 

 quartz and feldspars in the limestone. The average specific gravity of the whole* 

 eastern phase is about 2-700. 



Moyie Formation. 



The youngest member of the Purcell series is exposed on the western 

 slope of the Moyie river valley, where it crosses the Boundary line, and again 

 on a strong meridional ridge immediately east of the Yahk river at the same 

 line. In both cases the exposed top of the formation is an erosion surface. 

 At the Yahk river section the base is cut off by a major fault. The thickness 

 of the formation as a whole cannot, thejrefore, be stated. At the Moyie river a 

 maximum thickness of 2,200 feet was observed; at the Yahk river the estimates 

 varied from 3,100 feet to 3,700 feet. The safest of the larger estimates may 

 be placed at about 3,400 feet, which is a minimum thickness. 



The formation is here considered as including, at the sumimit, the Yahk 

 quartzite, which was proposed as a formational name in the summary report 

 for 1904. On later study of the sections it has appeared advisable to withdraw 

 the name ' Yahk quartzite ' from the list of Boundary formations. The rocks 

 to which it refers crop out only at one place in the belt; in composition they 

 are rather closely allied to the overlying beds; thirdly, they are not specially 

 well exposed, are warped and broken, and are limited above by an erosion 

 surface, so that, clearly, the whole thickness cannot be found in the Boundary 

 belt. 



The upper 400 feet of the Moyie formation as redefined are chiefly composed 

 of whitish and gray quartzites, with metargillitic intercalations. The lower 

 3,000 feet form a somewhat heterogeneous assemblage of argillites, metargil- 

 lites, and impure quartzitic or cherty rock in rapidly alternating" beds. The 

 strata are, on the average, much thinner than those of the underlying forma- 

 tions, running from a small fraction of an inch to a couple of feet in thick- 

 ness. Though many of the thinner laminae are often aggregated in plates six 

 inches thick or more, these rocks are of a decidedly fissile habit. 



The argillites are often true shales, but probably most of the beds must 

 be referred to true metargillite. Their colour varies from light gray to very 

 dark gray or black; the colours of weathering are brown and gray. At the 

 Moyie river locality several hundred feet of the shales occurring at the base 

 of the formation are sandy and have a dark purplish-red colour, owing to a 

 special content of oxide of iron. A few, very thin (1 to 2 mm. thick) layers 

 of red hematite were observed in these purplish strata. The latter merge 

 gradually into the underlying conformable Kitchener formation. The inter- 

 bedded quartzites are always very fine-grained or compact, of a light gray 

 colour on fresh fractures and gray, brown, and light buff on weathered surfaces. 

 Many of the quartzites are argillaceous. Some of the beds are charged with a 

 variable amount of calcium and magnesium carbonates, which were also found, 

 by tests in the laboratory, to characterize specimens of the gray shales. The 



