8 A POPULAR EXPOSITION OF THE 



Mingan Islands consist chiefly of the Chazy formation, the Trenton 

 beds appearing at the south side of Large Island, one of the group. 

 The northern shore of the Island of Anticosti is made up of Hudson 

 River beds, the rest of the island consisting of Middle Silurian strata. 

 In Gasp6, the Hudson River formation occurs on the north shore, be- 

 tween Cape Rosier and the River Marsouin. Eastward and southward 

 the peninsula is chiefly composed of strata referred to the Devonian 

 Beries, in which a thin seam of coal and numerous fossil plants are met 

 with ; whilst along the Bay of Chaleurs and the coast south of Gaspe 

 Bay, the inclined Devonian beds are overlaid unconformably by a vast 

 thickness (amounting to no less than 300 feet) of Carboniferous sand- 

 stones and conglomerates, the Bonaventure Formation of Sir William 

 Logan. These strata, however, are quite destitute of coal. 



Mountainous masses of eruptive traps and trachytes occur towards 

 the more western extremity of the St. Lawrence Basin. These break 

 through Lower Silurian strata, and were formed, probably, during the 

 Upper Silurian or earlier part of the Devonian epoch. They are tra- 

 versed in most cases by dykes of more recent origin — apparently 

 erupted towards the close of the Devonian period, or perhaps at a still 

 later date. The more important of these intrusive masses, comprise : 

 Rigaud (in Vaudreuil Co.) ; Mount Royal or the Montreal mountain ; 

 Montarville or Boucherville (in Chambly Co.) ; Rougemont (in Rou- 

 ville Co.) ; Belceil (in Vercheres Co., near the Grand Trunk Railway) ; 

 Monnoir or Mt. Johnson, south of Belceil ; and Yamaska. Other 

 masses of a similar character, as those of Brome and Shefford, lie just 

 within the Eastern or Metamorphic Basin ; but as these are evidently 

 connected with the above series, the whole may be described together. 

 The moimtains of Montreal, Montarville, and Rougemont, are essen- 

 tially augitic traps or dolerites. They present a dark color in most 

 parts, and contain, in many places, distinct and comparatively large 

 crystals of augite ; Fig. 251. Small granular masses of olivine, with 

 black grains of Magnetic Iron Ore and Ilmenite (mine- 

 rals described in Part II.) are also commonly present, 

 especially in the Montarville and Rougemont mountains. 

 These trappean masses are penetrated by dykes of white 

 or light-coloured compact trachyte (see Part III.), which 

 contain minute crystals of iron pyrites, and generally eflFer- 

 Fig, 251. vesce in acids from the presence of intermixed carbonate of 

 lime. The Rougemont mountain, is traversed also by granitic trachyte 



