85 



Augite porphyrite. — The augite porphyrite series 

 forms a large part of the area originally mapped as the 

 Rossland volcanic group. It occupies four main areas 

 on the map sheet and is intrusive in the Mount Roberts 

 formation. The structures and textural characteristics 

 of the rock shows that it probably occurred as surface 

 flows and sills. In places the rock is interbanded with 

 fine-grained beds which are probably tuffs. In other 

 places it presents an agglomerate phase of two eruptions. 

 The typical rock is dark grey to greenish black, studded 

 with stout prisms of pyroxene and hornblende imbedded in 

 a dark ground-mass composed chiefly of small laths and 

 grains of labradorite and hornblende. The rock is both 

 massive and sheared and in places is highly altered. An 

 analysis of a type from the War Eagle is as follows: — 



SiOa 50-89, TiOa o-8o, AI2O3 17-00, FeoOs 0-97, 

 FeO 7-6o, MnO 0-14, Mg0 5-4i, Ca0 9-82, KaOi-si, 

 Na20 3-35, H2O- o-o6, HaO + i-H, P2O5 0-19, S 0-43, 

 CO2 o • 28 = Total 99 • 39. 



Triassic ? 



The Volcanic agglomerate of probably Triassic age 

 overlies the Mount Roberts formation, apparently conform- 

 ably. The outcrop is lenticular in form and coincides 

 in strike and vertical dip with the underlying slates. 

 The formation suffered with the Carboniferous in the 

 crustal disturbances of the Jurassic revolution. 



The agglomerate is composed of fragmental material 

 including quartz, slate and altered volcanic rocks. The 

 formation also includes some tufaceous beds. There 

 is a rough assortment of the material in certain beds, 

 in which cases the longer axis of the fragments coincide 

 with the general strike of the formation. 



Jurassic 1 



Monzonite. — ^The monzonite intrusions, in the forms 

 of masses and dykes, are composed of a number of closely 

 related varieties of slightly different ages which underlie 

 about one half of the Rossland map-area. The intrusive 

 masses have an east and west trend and have possibly 

 followed a profound structural break. The structural 

 relations show that the intrusion was subsequent to the 



