170 G. M. DAWSON — STRUCTURE OF THE SELKIRK RANGE. 



resemblance of the formations to those met with in the Rocky Mountains is 

 in itself sufficient to enable some important general conclusions to be arrived 

 at respecting the rocks of the Selkirk range, while the ai^alogy of the rocks 

 of the Selkirks to those of the first section is also such as to afford some clue 

 to the age of the formations represented in it. 



The Shusiuap Series. — The lowest crystalline, and presumably Archean, 

 rocks largely represented in the western portion of this part of the Selkirk 

 range are evidently referable to the Shuswap series of the first section. 

 They consist chiefly of gray gneisses, varying from nearly massive to quite 

 schistose, and in the latter case frequently having their division-planes 

 thickly covered with glittering mica. They are both hornblendic and mica- 

 ceous, but the last-named mineral usually preponderates. Orthoclase is 

 apparently the most abundant feldspar, quartz is nearly always well repre- 

 sented and garnets are not infrequent. In many places nearly half the 

 entire mass of the rocks exposed consists of intrusive or vein granite, with 

 pegmatitic or graphitic tendencies. 



The Nisconlith Series. — Overlying the basal holo-crystalline series in the 

 Selkirk section is a mass of rocks of which the thickness is estimated at 

 15,000 feet. These are dark-colored and generally blackish argillite-schists 

 and phyllites, representing various stages in alteration between true^argil- 

 lites and micaceous schists. The rocks are usually rather finely fissile, with 

 gh)ssy and sometimes wrinkled surfaces, but often with much minute yet 

 visible mica on the division-planes. These planes are in some cases evi- 

 dently due to cleavage, but are often true bedding-planes. The rocks are 

 usually calcareous, and frequently hold thin layers of dark-bluish or black 

 impure limestone, together with occasional layers of dark quartzite. The 

 coloration is evidently due to carbonaceous matter, and pyrites crystals 

 are very common in certain zones. The only notable diversity met with in 

 this otherwise homogeneous mass of rocks is found towards the base, where 

 (at the lower end of Albert caiion) a bed of pure blue-gray crystalline lime- 

 stone thirty feet or more in thickness occurs, and a short distance still lower 

 in the section, a series of beds over 1,000 feet in thickness, consisting chiefly 

 of granular pale-gray quartzites. The quartzites are sometimes flaggy and 

 generally more or less micaceous, and are interbedded as well as overlain 

 and .underlain by blackish micaceous argillites and layers of coarsely mica- 

 ceous pale schists. 



These rocks undoubtedly represent the Nisconlith series of the first column, 

 of which no extended sections have yet been found in the interior plateau, 

 while to the eastward they certainly correspond in the main with the Bow 

 River series of the Rocky Mountjaius, for which a thickness of 10,000 feet 

 was there ascertained, though the base of the series is never exposed in the 

 Rocky Mountains. 



