Dresser — Geology of Br ome Mountain. 347 



Art. XXXI. — On the Geology of Brome Mountain, one of 

 the Monteregian Hills / by John A. Dkesser. 



(Published by permission of the Director of the Geological Survey of Canada.) 



In the western part of the province of Quebec, the basin 

 between the Appalachian Hills on the southeast and the south- 

 ern edge of the old, but now elevated, Laurentian peneplain* 

 at the northwest, is about eighty miles wide. It is occupied 

 by rocks of Paleozoic age in which the geological scale is repre- 

 sented from Cambrian to Lower Devonian, both inclusive. This 

 basin has a nearly level surface except for the presence of a 

 series of hills, eight in number, known as the Monteregian 

 Hills.f Six of these, namely, Mount Royal, Montarville, Belo- 

 eil, Rougemont, Yamaska and Shefford, rise at somewhat regu- 

 lar intervals of about ten miles, and in a nearly east and west 

 line. They thus extend for a distance of fifty miles eastward 

 from Mount Royal and from the city of Montreal at its base. 

 Brome Mountain and Mount Johnson are respectively two and 

 a half and six miles south of Shefford and Beloeil. Mount 

 Royal, which is probably the lowest, is 769*6 feet above mean 

 sea level, while Shefford has an altitude of 1,600 feet. Rouge- 

 mont, Montarville and Yamaska have not yet been determined. 

 The others are intermediate between the heights given, Brome 

 reaching an altitude of 1500 feet. 



Considered physiographically, these hills are of residual ori- 

 gin, having been etched into their present relief by the exten- 

 sive denudation of the region by which not less than one thou- 

 sand feet of the plain have been removed. The composition 

 and texture of the rocks which compose these hills have 

 evidently offered so much greater resistance to denuding agen- 

 cies than was afforded by the surrounding strata as to give the 

 hills their present elevation. Hence they are hills of the butte 

 type. 



Reports on the geology of the district, with more or less 

 attention to the petrography of these hills, have been made by 

 Dr. T. Sterry Hunt in 1858, by Sir William Logan in 1863 

 aud by Dr. R. W. Ells in 18944 



Dr. F. D. Adams in 1903§ made a general review of these 

 hills and proposed for them the name "Monteregian", (Mons 

 Regius), and also gave a detailed description of Mount Johnson. 

 Fig. 1 of this sketch is reproduced from Dr. Adams' paper. The 

 writer is also indebted to Dr. Adams for valuable advice on 

 many points in connection with this investigation. 



* Dr. A. W. G. "Wilson, Journal of Geology, vol. xi, No. 7, "The Laurentian 

 Peneplain." 



+ Dr. F. D. Adams, Journal of Geology, vol. xi, No. 3. "The Monteregian 

 Hills — a Canadian Petrographical Province." 



X Geological Survey of Canada. § Op. cit. 



