150 DEPARTMENT OF THE INTERIOR '' 



2 GEORGE V., A. 1912 



much limonite disseminated through the cement, are the usual subordinate 

 minerals. The clastic grains, large or small, are characteristically angular and 

 the rock as a whole, may be classed as a metarkose. Many of the quartz grains, 

 though several millimetres in diameter, are fragments of single crystals, show- 

 ing that their source was doubtless a very coarse granite. 



Zones b and d are in composition simply finer-grained, gritty equivalents 

 of zones h and j. The former zones seem to be more massive than the latter 

 and less sheared or mashed. Nevertheless, the thin sections are replete with 

 evidences of the great stresses which have operated on all these rocks. The 

 quartz grains and pebbles always show undulatory extinction or granulation. 

 Owing to this minute Assuring and the resulting partial decomposition of light 

 reflected from the interiors of the glassy grains, the quartz is commonly opales- 

 cent in bluish tones which are sometimes quite deep and pure. 



The average specific gravity of two specimens of the conglomerate-sand- 

 stone zones is 2-640. The average of four specimens of the schists is 2-717. 

 Allowing for the relative thickness of these rock-types, the average specific 

 gravity of the whole formation may be placed at about 2-705. 



Wolf Formation. 



Zone a of the Monk formation is conformably overlain by a mass of very 

 heavily bedded sandstones, grits, and fine-grained conglomerates, which in all 

 essential respects are identical in character with the coarser-grained phases of 

 the Monk formation. On account of its thickness and conspicuous nature this 

 mass has been distinguished by a special name, the Wolf formation. 



Its exposures are unusually perfect in the broad band crossing the ten-mile 

 belt from Mt. Ripple northward to the headwaters of Wolf creek. The out- 

 crops are especially extensive along the Dewdney trail at the summit of the 

 range and, again, on the south-eastern flank of Mt. Ripple* At the last named 

 locality the beds stand vertical or nearly vertical and there the formation can 

 be best studied. Some uncertainty must attach to measurements of thickness, 

 for this formation passes very gradually into the overlying Dewdney quartzite 

 and in none of the sections is the actual base exposed. At the Mt. Ripple 

 section the total thickness was measured at 2,900 feet and this seems to be 

 steadily held throughout the Boundary belt. 



The formation is more massive than any other sedimentary member of the 

 Summit series; where most massive it consists chiefly of a feldspathic quartz 

 grit or conglomerate which, for fifty or more feet of thickness at a time, shows 

 no conspicuous plane of bedding. In the lower two-thirds of the formation and 

 much oftener in the upper one-third, the grit or conglomerate is interrupted 

 by thin beds of metamorphosed, more or less argillaceous sandstone. Practi- 

 cally without exception the beds are of a medium gray or, less commonly, 

 greenish-gray colour on fresh fractures and weather a pure gray or brownish 

 gray. 



The larger pebbles of the conglomerate are composed of vitreous quartz: 

 sugary, gray or white quartzite; much more rarely, dark gray to blackish 



