518 J. A. DRESSER IGNEOUS ROCKS OF EASTERN QUEBEC 



railway at Bonaventure depot, Montreal, at the base of the mountain, is 

 48.33 feet. 



The mountain consists of two distinct intrusions, the first and larger 

 being essexite, the second nepheline-syenite. In structure it is thought 

 to be a volcanic neck, probably with laccolitic offshoots. It has may dikes 

 and sheets of bostonite, camptonite, tinguaite, and allied rocks. 



A breccia near by has an ash rock for its matrix and contains, among 

 other included fragments, some blocks of Devonian age. 



It is now under investigation by Professors Harrington and Adams. 



The area of Montarville, or Saint Bruno mountain, is approximately 

 2.64 square miles. The average of several aneroid readings shows its 

 altitude to be 563 feet — that is, 466 feet above the Grand Trunk Kailway 

 station of Saint Bruno. 



It consists of a single intrusion and is composed entirely of essexite 

 except for a small area of half an acre. This is occupied by a rock of the 

 pulaskite type, which has been formed by differentiation in situ from the 

 essexite magma. A few dikes of camptonite are found.* 



Beloeil, or Saint Hilaire mountain, has an area of some 4 square miles 

 and an altitude of 1,437 feet above sealevel, or 1,350 feet above the rail- 

 way near its base. It consists of a single intrusion, differentiated to 

 form essexite and a nepheline-rich syenite. The former rock makes up 

 the greater part of the mountain. 



A few dikes of camptonite are to be seen.f 



Eougemont occupies about 6 square miles and reaches a height of 1,400 

 feet, or 1,250 feet above the surrounding plain. As far as yet known, it 

 consists of one intrusion of essexite. No dikes are known. 



Mount Johnson, the smallest of the series, has an extent of .422 of a 

 square mile. Its altitude is 875 feet, giving it an elevation of 720 feet 

 above the neighboring village of Saint Gregoire. It is a volcanic neck, 

 differentiated from a core of essexite to a rim of pulaskite, with an 

 intermediate phase (andose).J 



There are only a few dikes. 



Yamaska hill covers some 5y 2 square miles. It greatest altitude is 

 about 1,500 feet, nearly 1,300 feet above the surrounding country. 



It has been found to consist of a single intrusion which has differen- 

 tiated in situ into rocks of the essexite-nepheline-syenite series. Dikes are 

 few.§ 



Shefford mountain occupies nearly 9 square miles and rises to a height 

 of 1,600 feet above sealevel, or 1,200 feet above the surrounding country. 



* J. A. Dresser : Summary Report, Geological Survey of Canada, 190~>. 

 f O. E. Le Roy : Summary Report, Geological Survey of Canada, 1901. 

 J F. D. Adams in Journal of Geology, vol. xi, no. 3. 

 2 G. A. Young : Summary report, Geological Survey of Canada, 1903. 



