[HOWARD] SOME OUTLIERS OF THE MONTEREGIAN HILLS 49 



nordmarkite and camptonite in the eastern part of the area in the 

 vicinity of Lake Memphremagog. 



Location of the Monteregian Hills 



In the St. Lawrence lowlands in the Province of Quebec, there 

 stand out prominently eight isolated hills spaced at more or less 

 equal intervals. These hills, known as the Monteregian Hills, extend 

 almost due east and west for a distance of about fifty miles. They lie 

 roughly in two parallel lines with a third cutting them at an angle 

 of about 30°. The parallel lines lie approximately west north-west 

 and east south-east, the northern series being composed of Shefford, 

 Yamaska, Rougemont, and St. Bruno, and the other containing Brome, 

 Mount Johnson, and Mount Royal. The intersecting line cuts these 

 at St. Bruno and Mount Royal and extends eastward to St. Hilaire. 



The cores of all these hills are composed of sodic igneous rocks 

 and are either volcanic necks, or laccoliths; besides these larger 

 masses, there are also small bosses, sheets, or systems of dykes or 

 breccias either in line with the main bodies or forming subsidiary 

 lines. Thus the Shefford-St. Bruno series can be extended eastward 

 to include the exposure at Eastman,^ and westward to include the 

 dykes at Sault au Recollet, Ste. Rose, and the sheet at Ste. Monique. 

 The Brome-Mount Royal series includes dykes at Chambly and 

 Farnham and extends eastward through Bolton Centre to Lake 

 Memphremagog where there are also associated dykes. West of 

 Mount Royal, this line includes the sheet at Ste. Dorothée. The 

 St. Hilaire-Mount Royal line spreads out to the west and includes 

 all the breccias described by Harvie and the alnoites and associated 

 rocks at Ste. Anne de Bellevue, Isle Cadieux, and La Trappe. 



A similar grouping in lines running north and south is apparent. 

 Ells' suggests that the intrusives lie on a parallel series of north- 

 south faults. Thus lines joining Shefford and Brome, St. Hilaire, 

 Johnson and the dykes around Lake Champlain, and the line joining 

 the extreme western outliers are all parallel and lie in the direction 

 suggested by Ells. There is, however, little direct evidence that hese 

 lines represent lines of faulting, but it is quite probable that the 

 intrusions took place along lines of weakness or deep-seated fracture. 



^J. J. O'Neill, St. Hilaire and Rougemont Mountains, Quebec, ^emoir 43 

 G.S.C., p. 8. 



2R. W. Ells. Report on the South West Sheet. Eastern Townships Map, Ann. 

 Rep. G.S.C. Vol. VII, Pt. J, p. 73. 



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