every 25 feet (7-5 m.). The principal varieties are typical 

 minettes, kersantites, vogesites and odonites with many 

 intermediate forms [1]. Aplitic dykes also occur which 

 may be complementary to the more basic types. 



Tertiary. 



Pulaskite. — The pulaskite or alkali syenite occurs in 

 irregular, elliptical and dyke-like masses intrusive in all 

 the older rocks. Some of the present outcropping masses 

 may represent deeply eroded conduits of ancient volcanoes. 

 The normal rock is coarse in grain and pale pink in colour. 

 It is composed essentially of long rectangular feldspars 

 (intergrowths of orthoclase and albite) with biotite and 

 hornblende, though neither of the two latter are abundant. 

 An analysis by Dr. F. Dittrich, Heidelberg, gave the 

 following : — 



510262-59, Ti02 0-54, AI2O3 17-23, Fe203 1-51, FeO 

 2-02, MnOtr., MgO 1-30, CaOi-99, K20 6-74, NaaOs-so, 

 P2O5 o • 1 1 , U2O o • 30, CO2 tr., CI tr., SO3 tr. = 99 • 83. 



The rock is closely related in every respect to similar 

 intrusions at Phoenix and elsewhere in the Boundary 

 district which are of Miocene age. 



ORE DEPOSITS. 



There are two mineralized belts in the Rossland camp 

 known as the North and South belts respectively. The 

 North belt is by far the most important. All the rocks 

 except perhaps the later dykes are more or less mineralized, 

 but the large ore bodies are confined mainly to the Car- 

 boniferous augite porphy rites and the monzonite, and lie 

 along the northwest border of the large area of monzonite, 

 and near or on the contact of the porphyrites and Mount 

 Roberts formation with the monzonite, granodiorite 

 or granite porphyry. The South belt is underlain mainly 

 by the porphyrites and sediments of Carboniferous age. 



In the North belt, the ore deposits occur (a) in fissure 

 veins with or without replacement of the country rock; 



(b) as lodes in zones of fissuring or shearing, the ore minerals 

 forming a network of veinlets impregnating or replacing 

 in whole or in part the intervening masses of country rock; 



(c) in irregular impregnations in the country rock. The 

 most important ore bodies found so far have occurred as 



