REPORT OF THE CHIEF ASTRONOMER 123 



SESSIONAL PAPER No. 25a 



The dominant colour on fresh fractures is throughout gray or greenish- 

 gray, weathering to a somewhat lighter tint of nearly pure gray. A few white 

 or grayish-white beds occur irregularly through the formation and, also rarely 

 greenish-gray beds weathered light rusty-brown or reddish-brown, so as to 

 resemble typical Kitchener quartzite. 



Heavier beds characterize the formation where its upper part crops out 

 just east of the cliff. That seems to te the rule for the quartzite generally as 

 it is exposed in the Purcell range; the bedding is thick and massive in the top 

 and bottom divisions and thinner-bedded in the middle division of the strata. 

 The exposures, however, are nowhere continuous enough to allow of a trust 

 worthy estimate of the relative strength of these three divisions. 



The sediment sometimes, though quite rarely, shows cross-bedding. 

 Sun-cracks, rill-marks, ripple-marks, and annelide burrows were not identified in 

 a single case among the strata exposed on McKim cliff. Elsewhere within the 

 Boundary belt these markings were found; rarely in the dominant quartzite, 

 but more particularly in the metargillitic horizons. 



Already in the hand-specimens numerous glints of light from non-mica- 

 ceous particles suggest that the rock is highly feldspathic. At thcsame time it 

 is seen tbat the general greenish tint of the quartzite is due to disseminated 

 minute plates and shreddy foils of mica. These observations are confirmed by 

 microscopic examination. Interlocking quartz, feldspar, and mica are seen to 

 be the essential constituents. Each of these minerals is glass-clear in the fresh 

 specimens. Orthoclase, microcline, microperthite, oligoclase, and probably 

 albite make up the lis* of feldspars. Of these orthoclase and microperthite are 

 the most abundant, though it is not certain that, in any specimen, the other 

 feldspars of the list are absent. The mica includes both highly pleochroic 

 biotite and muscovite, the latter being either well developed in plates or in 

 the typical shreds of sericite. In some specimens the biotite is the more abund- 

 ant of the two micas but in others it tecomes subordinate to muscovite and 

 may disappear altogether. 



Other constituents are very subordinate; they include rare anhedra of 

 titanite, titaniferous magnetite, pyrite, epidote and zoisite. 



The quartz and feldspar grains vary from 0-02 mm. to 0-2 mm. in diameter, 

 averaging perhaps 0-06 or 0-08 mm. The lengths of the mica scales are usually 

 not much greater. Though few direct traces of clastic form are left among 

 the minerals, it is probable that these dimensions represent approximate^ the 

 size of the original grains. The texture of the quartzite is thus, quite fine in 

 the type specimens as, indeed, throughout all the exposures; in all the thousands 

 of feet of thickness no conglomeratic, gritty, or even very coarse sandy bed 

 was seen. 



It is an open question, perhaps, whether this rock should be called a 

 quartzite if by that term, we mean an indurated sandstone. The average 

 quartz grain is much, too small to have formed originally a true sand. In fact 

 the average grain of the rock is not more than one one-thousandth as large 

 a? the average grain of typical beach sand. The name ' quartzite', adopted 



