REPORT OF TEE CEIEF ASTRONOMER 149 



SESSIONAL PAPER No. 25a 



strike, N. 12° E., gave, respectively, 30° E. and 55° E. for the dips. There 

 is evidently some crumpling, especially in the fine-grained phases, but on the 

 whole, schistosity and bedding seem to be very nearly coincident throughout 

 the formation; their planes are seldom far from the vertical. 



The natural suspicion that so great a thickness of fairly homogeneous, 

 schistose rocks might be, in part, explained by duplication was not strengthened 

 by the data secured during four different traverses over the section. The poor- 

 ness of the exposure makes it unsafe to exclude the possibility that there is 

 duplication, but the fact that the band of rocks belonging to this formation 

 conserves its width as it is followed from the Boundary line northward for 

 six or more miles, affords some evidence against the idea of repetition of beds. 

 If the faulting or folding had repeated these particular beds to any great 

 extent, we should expect the beds of the conformable Monk grit and Irene 

 Volcanic formation to show strong local deviation from the regional strike. 

 On the contrary, the contact-lines of these formations run remarkably straight 

 for the whole six miles across a very mountainous area. The simplest, as well 

 as the most probable, conclusion is that these three great formations all belong 

 to one conformable series locally upturned in a single monocline and that in 

 no one of them has there been duplication by either folding or faulting. 



The greater part of the formation is composed of quartz and sericite in 

 variable proportion. The original composition of the dominant fine-grained 

 rocks ranged from compact quartz sandstone to argillite. For hundreds of 

 feet together in each of zones c, d, g, and i, the beds are made up of sheared 

 sericitic, light greenish-gray quartzite. This phase alternates with darker 

 greenish-gray, highly fissile schist in which metamorphic mica (sericite and, much 

 less abundantly, biotite) equals or dominates the quartz in amount. Within 

 these limits there is great uniformity in the formation except for the occur- 

 rence of the gritty or conglomerate zones. The usual accessories, magnetite, 

 pyrite, chlorite, etc., are present but are always quantitatively unimportant. 

 Eeldspar has not been observed and if, as is probable, it was originally acces- 

 sory in the quartzitic phases, it has itself been sericitized. The monotony in 

 the mineralogical composition of these schistose rocks is known to be broken 

 only in zone e, where well crystallized cyanite in simple twins, has developed 

 in some abundance. 



Zones &, d, h, and ], totalling about 700 feet in thickness, are made up of 

 detrital materials which are fairly uniform in composition though not in grain. 

 Zone j is a greatly mashed gray conglomerate with pebbles of quartzite and 

 black slate, pressed or drawn out into lenses up to four or five inches in length. 

 Pebbles of dolomite were not seen but this rock is very similar to common 

 phases of the Irene conglomerate. The matrix of the pebbles is again phyllitic. 

 Zone h is a conglomerate of the same type, though bearing sandy and gritty 

 phases which are strongly feldspathic. A thin section from a coarse arenace- 

 ous specimen showed that glassy quartz, much typical microperthite, ortho- 

 clase, basic andesine, some microoline in a cement of shreddy muscovite, and 

 a little chlorite formed the principal constituents. Euhedra of magnetite and 



