514 J. A. DRESSER IGNEOUS ROCKS OF EASTERN QUEBEC 



sequently that the quartz-porphyry and serpentine are differentiates of a 

 single original magma. As these are the extremes of chemical composi- 

 tion among the various rocks of the region, the probability of all being 

 differentiation products of a single primary magma is quite apparent. 



The Granites 



The granites of the Eastern townships occupy six principal areas, none 

 of comparatively great extent. They form the granite masses of Stan- 

 stead, Hereford mountain, Big Megantic mountain, Little Megantic 

 mountain, a small area on the east side of lake Memphremagog, and 

 another near Danville. There are probably numerous other small occur- 

 rences in this district, but it is noticeable that all of the granites lie to 

 the south of the volcanics of the Sutton ridge. 



None of the granite bodies have as yet been studied in detail, but all 

 are believed to be intrusive through Lower Silurian sediments, and are 

 thought to be of late Devonian age. The extensive quarries at Stanstead 

 have made the economic importance of that occurrence well in the prov- 

 ince of Quebec, where Stanstead granite is largely used for structural pur- 

 poses. A specimen of this granite has been described by Dr F. D. 

 Adams,* and shown to consist essentially of orthoclase, quartz, and biotite, 

 with accessory amounts of microcline and plagioclase and secondary mus- 

 covite and epidote. 



Of Hereford mountain nothing definite is known, save that its prox- 

 imity to Stanstead and the generally similar appearance of the rock in the 

 hand specimen suggest its close relation to that body. Its contact with the 

 sediments is undoubtedly intrusive. 



Even less is known of the Big and the Little Megantic mountains. 

 The material in the talus slopes of the former is a very acid granite. 



The granite from Scotstown contains pyroxene, in addition to biotite 

 and muscovite, as ferromagnesian constituents. 



The granite near lake Memphremagog is also of the type of that of 

 Stanstead. 



Near Danville there is a small body of granite whose relations to the 

 surrounding rocks have not been ascertained, nor has it received any 

 detailed study. Biotite is the only dark constituent that is noticeable in 

 the hand specimen. It is stated in the Geology of Canada (page 811) 

 that it furnished part of the material for the Grand Trunk Eailway bridge 

 which crosses the Nicolet river in the vicinity. 



•"Description of a series of thin sections of typical rocks," by Frank D. Adams, 

 Ph. D., F. G. S., Montreal, 1896. 



