Section IV, 1920 [7] Trans. R.S.C. 



Granitic Segregations in the Serpentine Series of Quebec 



By John A. Dresser, M.A., F.R.S.C, F.G.S.A. 



(Read May Meeting, 1920) 



General 



The area commonly called the "Serpentine Belt" of southern 

 Quebec is occupied by a series of ultra-basic rocks which run north- 

 easterly in a narrow, intermittent band along the Southeastern fîank 

 of the Sutton, or main, Appalachian axis, from the southern boundary 

 of the province to the Gaspé peninsula. These rocks are intrusive 

 through sediments of Cambrian and Ordovician, if not also some of 

 still later age. The series is remarkable economically as being the 

 chief source of the world's supply of asbestos, also for the production 

 of chromite; and, otherwise, for the wide range and uniformity of 

 differentiation exhibited by the rocks of which it is composed. 



Principal Rocks 



The principal rocks are peridotite, pyroxenite, and diabase. In 

 the mining areas, which as yet are confined to the counties of Megantic, 

 Wolfe and Richm.ond, their relations are fairly well known, and their 

 origin by differentiation from one magma, though probably intruded 

 at different periods in different parts of the "belt," is well established. 

 They occur as sills, stocks and bodies of intermediate shape, adjusted 

 to the attitude of the enclosing strata. In all forms, the principal 

 differentiates are arranged in the order stated above (that of decreasing 

 basicity and density), in sills, from the base upward; in stocks from 

 the centre outward.^ 



Minor and Secondary Rocks 



There are also lesser amounts of other rocks. Between p>Toxenite 

 and diabase there is frequently a zone of rock that would be more 

 precisely classed as gabbro. Diabase not infrequently passes into 

 porphyrite as its outer margin ; peridotite, in places of better differen- 

 tiation, becomes dunite; and other varietal distinctions might be 

 made. Amongst secondary rocks, pyroxenite altered to talcose 



^ This annular arrangement of differentiates in stocks, by which a core of perido- 

 tite is surrounded by zones of pyroxenite and diabase in outward succession, has 

 also been described by Duparc and Pamphile in the ultra-basic rocks of the Urals — 

 Comptas Rendus de la Société des Ing. Civ. — Paris, cir. 1910 



