8 THE ROYAL SOCIETY OF CANADA 



schists and serpentine, derived from peridotite, are abundant. The 

 latter gives its name to the series from its economic importance as the 

 country rock of the asbestos deposits. 



Granitic Rocks 



Besides the principal rock varieties and their allied and secondary 

 phases, there are numerous smaller dykes and irregular acid masses 

 which are generally of granitic character. In size they vary from 

 bosses occupying several acres to mere nodules or stringers an inch or 

 less in diameter. They are distributed without any apparent order, 

 but are, as far as known, confined to the peridotite-serpentine areas. 



Character: Lithologically the dominant material is a hornblende 

 granite which shows certain peculiar mineral relations, which serve 

 to distinguish it from the only other type of grantie known in the 

 region, which is the biotite-muscovite granite of Stanstead. In some 

 of the larger bosses, biotite is also present and the rocks become 

 coarsely porphyritic. In other phases the rock is aplite, or pegmatite. 

 Certain occurrences of lime silicate minerals, vesuvianite, garnet, and 

 diopside, also probably belong to this group. 



Relations: In many cases these peculiar rocks occur in the form of 

 small dykes, and they have been generally classed entirely as such in 

 published descriptions. The dykes are small, rarely exceeding 20 feet 

 in width, irregular in size and direction, and are seldom traceable 

 beyond a few hundred feet in length. They have not been observed 

 to cross one another. 



Irregular masses are numerous and variable in size as noted above. 

 In many instances it is difficult to say definitely in which category an 

 occurrence of granite should be placed, since there are wide gradations 

 in form as well as in size. 



As there is little differentiation evident in the smaller bodies, 

 whether dykes or irregular masses, it has been generally inferred that 

 all were injected while the country rock was still heated, and that they 

 are end products of intro-telluric differentiation of the general magma, 

 which were introduced at a somewhat later stage than the other mem- 

 bers of the series. From time to time, however, bodies of granite 

 have been observed, which appear to be completely isolated from one 

 another and which suggest an origin by magmatic differentiation 

 in place. Recent developments in mining also have afforded further 

 information which goes to confirm this view. So on the whole it 

 seems advisable to review the relations of these rocks. 



Until recently, mining was carried on almost entirely by open-cut 

 methods, or quarrying. Consequently only one surface of the rock 



