154 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



The steady occurrence of the dark-coloured, once-argillaceous beds in the 

 sandstone suggested the name ' Lower Banded Quartzite ' as an early designa- 

 tion for the formation in the field notes. The analogous name ' Upper Banded 

 Quartzite ' was similarly used for the Beehive quartzite which likewise shows 

 marked alternation of dark and light silicious beds. 



The quartzite is similar in composition to the fine-grained phases of the 

 Wolf formation and needs no detailed description. The light-tinted, often 

 ripple-marked beds are almost entirely made up of thoroughly interlocked 

 quartz grains, between which a few sericite foils may be seen. These beds are, 

 as a rule, apparently very poor in feldspathic material, though it must be said 

 that the specimens collected are too few to afford complete microscopic 

 evidence on this point. The darker bands, which vary from a fraction of an 

 inch to several inches in thickness, are charged with some biotite as well as 

 with the dominant sericite, while the accessory magnetite grains are abundant. 



The conglomerate interbeds persist, with nearly constant thickness across 

 the entire ten-mile belt. Throughout that long distance they stand almost 

 exactly vertical and parallel to the banding of the quartzite. The exposures 

 are often very fine (Plate 19). From the higher peaks the dark bands of the 

 conglomerate can be followed with the eye for miles.* The vertical dip explains 

 the extraordinary straightness of the mapped outcrop of the formation as it 

 traverses mountain and deep canyon alike. At several localities the pebbles 

 of the 225-foot band are arranged in layers making angles of from 5° to 12° 

 with the contact planes of the band, clearly showing the imbricated, fore-set 

 bedding of the old beach. 



The pebbles are water-worn; the diameters are of all lengths up to one 

 foot, averaging three inches. They consist of glassy quartz, gray or greenish 

 quartz schist and, rarely, black slate. The schistose dark green-gray 

 cement is highly variable in constitution. Quartz grains and a few grains of 

 altered feldspar are subordinate clastic ingredients ; most of the cement is 

 composed of sericite, biotite, chlorite, and accessory magnetite. One deep- 

 green, compact specimen, without visible pebbles of any kind, proved on micro- 

 scopic examination to he made up almost entirely of felted chlorite in which 

 minute, angular, accessory grains of quartz could be seen. 



On the southeast slope of Mt. Ripple the alumino-magnesian cement has 

 been rather thoroughly recrystallized so as now to be a mass of intimately 

 interlocking anhedra of cordierite, 0-2 to 0-4 mm. in diameter. This mineral 

 encloses swarms of minute sericite foils and magnetite grains. Small lenticular 

 areas of granular quartz here and there occur in the thin section. The develop- 

 ment of cordierite at this point, three miles from the nearest intrusive granite, 

 would hardly have been anticipated. It is probably the result of thermal meta- 

 morphism by the underlying batholithic magma, of which the granite stock at 

 the Dewdney trail was a constituent part. 



The composition of these conglomerates is, on the whole, like that of most 

 of the conglomerates in the Wolf, Monk, and Irene formations; the younger 

 beds are, however, much less sheared and schistose than the older ones. 



