MONTEREGIAN HILLS 519 



It consists of essexite, nordmarkite, and pulaskite, the first comprising 

 about half of the mountain. Each rock is the result of a separate intru- 

 sion. Dikes are very numerous and belong to the bostonite-camptonite 

 series. The mountain is a laccolite.* 



Brome mountain is 100 feet lower than the neighboring mountain of 

 Shefford and occupies about 30 square miles. 



It consists of essexite, alkali-syenite, and a small body of tinguaite. It 

 has been formed by two or possibly three separate irruptions and is prob- 

 ably part of the laccolite of Shefford, which is only 2y 2 miles distant. It 

 has very few dikes, f 



Chemical Analyses of Type Eocks from the Monteregian Hills 



The following are analyses of rocks from the Monteregian hills : 



I II III IV V VI VII VIII IX 



Si0 2 48.69 48.85 53.15 44.00 65.43 61.77 57.44 59.96 55.68 



Al a O,.... 17.91 19.38 17.64 27.73 16.96 18.05 19.43 19.12 20.39 



Fe,O s ... 3.09 4.29 3.10 2.36 1.55 1.77 1.69 1.85 2.10 



FeO 6.41 4.94 4.65 3.90 1.53 1.75 2.70 1.73 1.95 



MgO.... 3.06 2.00 2.94 2.30 1.36 1.54 1.16 .65 .80 



CaO 7.30 7.98 5.66 13.94 .22 .89 2.66 2.24 1.92 



Na 2 5.95 5.44 5.00 2.36 5.95 6.83 6.48 6.98 9.18 



K 2 2.56 1.91 3.10 .45 5.36 5.21 4.28 4.91 5.34 



TiO a 2.71 2.47 1.52 1.90 .16 .74 1.97 .66 .60 



P 2 5 1.11 1.23 .65 .20 .02 .15 .60 .14 .06 



MnO 15 .19 .46 .08 .40 .08 .25 .49 .31 



CI 07 .04 



H 2 95 .68 1.10 .80 .82 1.10 1.03 1.10 1.50 



99.36 100.02 99.84 100.01 99.78 99.97 99.69 100.17 99.83 



I. Essexite (Essexose) Mount Johnson. 

 II. Essexite (Andose) Mount Johnson. 



III. Essexite (Akerose) Shefford. 



IV. Essexite (Hessose) Brome. 



V. Nordmarkite (Nordmarkase) Shefford. 

 VI. Nordmarkite (Nordmarkase) Brome. 

 VII. Pulaskite (Laurvikose) Mount Johnson. 

 VIII. Pulaskite (Laurvikose) Shefford. 

 IX. Tinguaite (Laurdalose) Brome. 



Genetic Eelations of the igneous Eocks 



A better knowledge of the igneous rocks of the Eastern townships, 

 especially of the granites and diabases, is necessary before their genetic 



* J. A. Dresser in American Geologist, October, 1901, and in Geological Survey of 

 Canada. 1899, part L. 



f J. A. Dresser in American Journal of Science, May, 1904. 



