87 



Porphyritic monzonite. — ^The porphyritic monzonite 

 occurs in masses and dyke-like bodies. The outlines 

 of some of the masses suggest in cross-section, pipe-like 

 chambers extending upwards through the Carboniferous 

 rocks and may possibly be portions of old volcanic conduits. 

 In some of its phases the rock resembles types of the 

 coarse monzonite. It is light grey and coarse in grain 

 with large stout prisms of green pyroxene, secondary 

 horblende, countless small rounded hexagonal flakes of 

 brown biotite and abundant andesine feldspar. Another 

 type consists essentially of augite, biotite, an alkali feldspar 

 and acid labradorite. 



Post- Jurassic (?) 



Nelson granodiorite and granite-porphyry. — The 

 important batholithic intrusion which underlies hundreds 

 of square miles in West Kootenay is represented on the 

 Rossland map by one irregular area and several small 

 masses with related dykes of granite porphyry. The 

 rock is light grey in colour, of uniform grain and is composed 

 of biotite, hornblende, quartz and abundant feldspar 

 chiefly of the plagioclase varieties. The age, as far as 

 the development at Rossland is concerned, can only be 

 referred generally to the period following the Jurassic 

 orogenic movement and prior to the instrusions of pulaskite 

 of the Tertiary. 



Serpentine. — ^The outlines of the serpentine areas 

 in the vicinity of Rossland suggest vertical stocks or necks 

 intruded into the disturbed and highly inclined sediments 

 and porphyrites of the Carboniferous. They appear 

 to occur along the probable line of weakness followed 

 by the intrusions of the monzonite. The exact age of 

 these altered basic plutonics has not been determined 

 beyond the fact that they are older than the Tertiary 

 pulaskite. 



Lamprophyric dykes. — The monzonite and grano- 

 diorite intrusions were followed by fissuring and dyking 

 on an extensive scale. A general northerly trend is pre- 

 served by the dykes although they cross, branch and 

 coalesce in a very intricate manner. The total number 

 of dykes must be very great for in some of the underground 

 workings of the mines they occur on an average of one in 



