io8 



is in agreement with well known cases of magmatic segre- 

 gation in intrusive rocks, where differentiation has taken 

 place prior to intrusion. 



The batholithic intrusions near Thetford character- 

 istically consist of a dome-shaped central mass of perido- 

 tite, bordered, or sometimes nearly surrounded, by an 

 erosion valley. The outer side of the central mass is 

 formed by a ridge of diabase, or porphyrite, which again 

 passes into breccia at its outer edge. 



It may be mentioned that an identical relation of 

 rock types has also been found in association with the 

 platinum bearing peridotites of the Ural mountains. 



BROUGHTON SERIES. 



The Broughton series consist of serpentine, soapstone, 

 and greenstone schists. They are the rocks containing, 

 and adjacent to, the asbestos and talc deposits of Robert- 

 son, East Broughton, and Broughton, and of several 

 isolated locations in the vicinity. 



The greater alteration of these rocks indicates that 

 they are possibly earlier in age than the Thetford series, 

 although this difference may also be due to a greater 

 degree of metamorphism. The sediments enclosing them 

 are the grey schists and quartzites, in no case the red 

 slates of the Sillery formation. It can, therefore, only 

 be said of their relations that, they are intrusive in, and hence 

 later than the L'Islet formation which conformably under- 

 lies the Sillery. 



ECONOMIC GEOLOGY. 



The minerals of economic value that have been found 

 in the serpentine belt are asbestos, chrome iron ore, talc, 

 antimony, copper, and platinum. Of these, asbestos 

 alone is at present being mined, the production of which 

 represents one-half of the total mineral production of the 

 Province of Quebec, and is upwards of 80 per cent of the 

 world's output of asbestos. Chromite has at times been 

 produced in considerable quantity, but the industry has 

 never passed the prospecting stage and at present opera- 

 tions have ceased altogether. Antimony and talc have 



