206 Canadian Record of Science. 



In the present paper it is proposed first to gather to- 

 gether the more important facts concerning the geology 

 of the Monteregian hills which are scattered throughout 

 these various publications, revising some of the earlier 

 work and embodying the results of later personal studies, 

 and then to describe in some detail one of these hills — 

 Mount Johnson — of which hitherto but little has been 

 known. 



PETEOGEAPHY OF THE MONTEREGIAN HILLS. 



Hunt distinguished four types of igneous rocks as con- 

 stituents of the Monteregian hills. These he classed as 

 trachyte, phonolite, diorite, and dolerite, respectively. In 

 this classification no distinction was made between rocks 

 occurring as dykes and the great igneous intrusions 

 which form the body of the hills ; differences in structure 

 resulting from mode of occurrence were not considered, the 

 classification being based upon mineralogical composition 



alone. 



Eecent investigations have shown that Hunt's names do 



not convey an accurate idea of the petrography of these 

 hills, nor do they set forth the interesting relationships of 

 the various rocks composing them. It is necessary for 

 this purpose to adopt a more modern nomenclature, for all 

 the mountains of the group are composed of a family of 

 consanguineous rocks, and taken together they present one 

 of the finest examples of a petrographical province hith- 

 erto discovered. They consist, furthermore, of a rather 

 rare class of rocks characterized by a high content of 

 alumina and alkalies, especially soda. 



The rocks forming the great intrusions which make up 

 the mass of these mountains belong to two well-char- 

 acterized types — one light in color, poor in iron-magnesia 

 constituents, and comparatively high in silica ; the other 

 dark in color, rich in iron-magnesia constituents, and with 

 a lower content of silica. 'They may be classed as follows, 

 if Eosenbusch's nomenclature be followed : 



